The Mori changes are a huge survivor buff... but also ruins the game a bit

It's not just that. The idea of Finisher Mori as a whole is simply unhealthy.

By hiding the Mori animation behind a 4k, it automatically incentivizes people to slug for the 4k...and we all know how fun and riveting it is.

Not to mention it also indirectly encourages proxy-camping/tunnelling, reduce Killer variety and perk variety in order to get that juicy animation (which I guarantee will get old really quick and will be met with more scorn than a normal 4k, it would be a matter of time before Mori animations are seen as a form of BM like "let me rub my victory in your face a bit longer with this cutscene") since when Survivors start to get better, weaker/slower/M1 Killers tend to struggle more and need to play more aggressively to compete.

Hiding Mori behind 4k is, in my opinion, only going to make people hate those animations and will make the game even less casual/newcomer-friendly than it already is.

There's a reason why the dreadful basekit Unbreakable was attempted alongside the previous Finisher Mori PTB: otherwise every single games would just end in a slugfest. Hell, during that PTB there were more bleedout games than normal even though people could get up because Killers wanted that animation after tunnelling the first 2 Survivors.

However, I have a possible idea to keep Finisher Mori BUT make it healthier;

What if you can Mori the last Survivor by your hand without needing a perk/offering BUT can only do so if said Survivor was downed AFTER hatch spawned (which means either a 3k was already achieved or everybody else got out). A Mori made in this fashion would offer a massive BP boost (further enhanced by Mori offerings which would keep their old effect alongside giving an incrementally higher BP bonus depending on rarity).

This would incentivize people to NOT slug for the 4k and play the match in it's entirety. This wouldn't affect those that already slugged for the 4k but would reward those that don't and take a gamble to win the Hatch race. This keeps the Finisher Mori but is also healthy for everyone.

I think you missed something in my post, I'll repeat it.

"If said Survivor was downed after Hatch spawned".

To get the mori, the Killer would have to kill everyone else (or everybody else escapes) while there is still one Survivor on his feet and down them after hatch spawned. If everyone is slugged when the Hatch spawns then the Finisher Mori becomes unavailable for that match.

Locking Mori behind a 4k is unhealthy, in an ideal world there would be no changes to the mori system since there's about a thousand things that require attention more urgently than that in the game. However BHVR wants to push their idea even though it was thoroughly rejected last time (and still is by the majority) so alternatives can be looked for.

Another alternative to fix slugging for the 4k would simply give a "insta-bleedout" button if slugged when there's only 2 Survivors left, everybody is slugged/hooked/caged, or if slugged for more than 2 minutes (unless getting slugged for the 4k or the Killer is trolling, there's really no reason to be slugged for so long).