How did killers manage to win when gen lasted for 80 seconds?

Increase in gen efficiency evens the playing field.

If more Survivors did gens efficiently 2 years ago, the average game would be much shorter.

I highly doubt game balance changes affected them or anything, it's just time made them better

Basekit BT + new OTR, in addition to other perks granting survivors 15 extra health states, without even considering giving killers basekit Lightborn, makes the game harder for survivors?

Well avg survivor chase/macro was way worse, there were still strong regression perks, and you couldn't stock up on a trillion strong items/addons as easily.

The basekit was worse, but the slowdown perks were better. 25% + 60s Pop, 200% Ruin (or even skillcheck Ruin if you wanna go that far back), guaranteed 2 minute Corrupt.

You'd see Pop basically every single game for a period of time. Then it was Ruindying. Now it's Pop + Pain Res.

Some form of slowdown has always been meta ever since Hex: Ruin released.

If you are good at the game, you can win most of your killer matches without any perks whatsoever. Not even tie, not "compete" - win, 90-100% of your matches, many of them decisively. Not just not using slowdown perks, not using any perks, nothing to help in chase, no info perks, no stealth, nothing. This has been proven time and again throughout the years by good killer players on streams, including years and years back when the game was objectively much more survivor-favoured. Knightlight most recently did a "3/4k on every killer without perks/add-ons" streak, obviously completing it on the first attempt. Off the top of my head I know two more streamers that recently did similar things, namely Lionnek and Kaiizoru. I myself sometimes go loadoutless, play in a gloves-off manner, and win much of the time doing so.

This is not to say the same would be true if you actually faced equal opposition that is also armed to the teeth, but that simply factually almost never happens for good players. Even just facing 4 decent survivors is vanishingly rare, such that even really rather mediocre killer players win decidedly more often than not.

The announced slowdown nerfs are inconsequential for good killer players, and even just decent killer players will be perfectly fine (especially when keeping in mind that winning every match is of course not a reasonable target). It might have more of an impact in the mid-range, but then not only are there also survivor perk nerfs here, but the slowdown nerfs are really rather negligible in themselves.

Deadlock loses 5 seconds per activation, so it will lose a total of 20 seconds slowdown out of 120. As if 20 seconds are going to completely change a match. Yes it can have an impact at times, but it's unlikely to on average, and it also has to be kept in mind that the 5 seconds only matter if a survivor is actually at the gen the very moment it unblocks, which is not what usually happens as survivors venture out to do other things during the block time. There can actually also be edge-cases where the shorter Deadlock time can benefit the killer, such as by allowing them to earlier use regression perks on that gen (including Pain Res), as well as making it so the same gen gets Deadlock'd twice in a row when otherwise it could have still been blocked from a previous Deadlock proc, preventing it from getting blocked again. Grim Embrace loses 2 seconds per proc, 6 seconds in total, so it goes from 76 seconds of blockage to 70, a reduction of a couple percent. And this again only matters if a survivor actually is at the gen the moment it unblocks, which is more typical for Grim but still far from what happens every time, Grim too will often lead survivors to leave the gen to do other things and return more than 10 or 12 seconds later. I will say that I absolutely don't think these perks needed nerfs, and any second lost here does feel annoying, but again, it won't have much of an impact.

Pain Res goes from being able to regress 100% of gen progress to 80%, which I do find is a more significant change, especially because it as opposed to the aforementioned perks is not a guaranteed proc (you need to get to a Scourge hook), and because it might not even get its full regression power simply due to a gen it applies to not having 25 or 20% worth of progress. While it has to be noted that Pain Res does more than the initial regression (it can also cause a progress freeze for 3 seconds, as well as continual regression of course), I think this nerf is not good. It may be the most popular killer perk, but it's also a healthy perk that encourages spreading hooks early (to an extent anyway; this aspect of the perk - and various other perks - could definitely be honed in on more) as well as leaving the hook to pressure the affected gen (as opposed to gen blockage perks that you can get full value out of even when camping). I would also argue that Scourge perks should be strong not only because they are a perk type, but because that creates an interesting dynamic with Sabo strategies, something the devs have always seemingly wanted to be more relevant, and are buffing in this very patch. If anything, Gift Of Pain and Floods Of Rage (and Monstrous Shrine) should get buffed. Gift Of Pain at the very least needs compensation for the Mangled/Hemorrhage nerf.

The Weasel nerf is the most significant out of all of these, but at the same time I think this is also the one perk that needed nerfs. It has no limit to its potential procs (well, hooking and regression events, but once either comes into play with regards to Weasel the game is already won) and can regress up to ~30 seconds at a time. It really is ridiculously strong and doesn't even have any "healthy" aspects of encouraging spreading hooks or not returning to camp and tunnel after kicking a gen. While I would have wished for them to nerf strong slowdown perks like these in a way where they get worse if the killer is tunnelling (and better if they're not), such as in the example of Weasel perhaps making it 30% regression on first hooks of a survivor, 20% on second hooks, and 0% on third hooks, or only being able to cause regression on the gen furthest from the hook that has progress (highlighting its aura for the killer, causing 40-50% of regression if they kick it), I don't mind this nerf and think it is called for.

These slight nerfs will be more noticable in builds where people stack multiple of them, but that's a good thing because stacking slowdowns has always been a problem. It can also be pointed out that there are still really potent slowdown perks that have not been touched, such as Corrupt, Dead Man's Switch and its synergies, Pentimento. Although I will also say that I miss buffs to lesser slowdown perks here. As it stands, this is really a poor excuse of a "meta shake-up" attempt, where people will just keep using the same perks because they are still the best, just ever so slightly worse than they had been. It almost feels as if BHVR simply included all of these miniscule number changes to some of the most popular perks to make the update look more significant than it is. I would like to see improvements for Call Of Brine, Overcharge, Ruin, Surge, Oppression and Eruption, all of which (except for Ruin of course) have been compromised by the regression event system. COB and Overcharge were overnerfed, but with Eruption not being what it used to be, these two perks deserve to be better. COB could be 200% again, for its 60 seconds. Overcharge should either have a more difficult skill check (half or at least only 66% of its current size), or cause the continual regression to grow from 100 to 150% base regression. Eruption has been hit particularly hard by the regression event limit, it at the very least could do with a change where instead of regressing affected gens and incurring a regression event, it either blocks the gens for 15 seconds or causes a 50% repair speed debuff on the gens for 20-30 seconds (still causing continual regression in either case). Oppression simply does not need its ridiculous cooldown. I think it could even exist without a cooldown altogether, again all the more so in the regression limit reality we are in now. And Ruin in my opinion should be 200% base regression again, albeit also automatically disabling itself again if a survivor dies. Surge could also proc on downs achieved through special attacks.

Actual viciousness

It's remarkable that no one remembers old Moris.

Oh lord I remember when I first started playing. It was just a little before Leatherface came out. If we got hit with thana and the rare user of dying light it felt like game over lol. First hook felt horrible and got worse from there.

I still boon, cleanse totems and oopen chests.

While I agree with you overall, it's worth mentioning that healing times were NOT nerfed across the board. That change was on the 6.7.0 PTB, but it was scrapped before coming to live, being replaced with the medkit nerf we actually got.

For the record, you're right to say that killers don't NEED slowdown and these nerfs aren't going to make killer gameplay impossible, but that specific example of why isn't true.