Review Prove Thyself/BNP Change
In the past few updates, killers have received many changes to gen regression perks. Some received some nerfs, some received some strong buffs, while others were changed completely. Right now, I'd say at least one third of killers (if not more) are using some combination of Scourge Hook: Pain Resonance, Pop Goes the Weasel, Jolt, Thanataphobia, Call of Brine, Hex: Pentimento, and even Eruption. I'd say the most common is Resonance + Pop or some sort of grueling Pentimento full hex build. With Resonance + Pop, assuming they're both tier three, that's 55% of a gen's progress being taken away. Sure, Resonance only works four times, but it's still a very punishing combo especially early on in the game. Even then, Pop's 30% gen regression is still quite over-tuned and no surprise on why it is so popular lately. Pentimento is also very popular and is extremely punishing when paired with other hex perks that it becomes extremely difficult to combat as a survivor. Not even mentioning the three-genning that's been all too popular lately (this has been covered by many in other threads).
All this said, nerfing both the Brand New Part + Prove Thyself really restricts a lot of pressure that the survivors can make typically early on in the game (usually the only time that the survivors can actually build pressure). BNP's in particular pretty much get used right away in a match. Assuming a killer gets Resonance off pretty quickly, maybe even a Pop, that's greatly surpassing what a BNP would even provide pre-nerf you're proposing. It really is one of the last remaining add-ons survivors can take to create some level of pressure early on. Not to mention, the add-on isn't really all that widely used considering how rare they are to come by (I'm nearly P100 on a survivor and do not have that many BNP's). With the proposed changes to BNP's, they become even less appealing. The only way to make them more appealing with these changes is changing them from a pink (ultra-rare) item to a purple (very rare) item.
I won't go into much detail with Prove Thyself as it's been covered in a lot of threads already. Prove Thyself was in a comfortable spot. Its value is really only strong early on when all survivors start fairly close together. As the game progresses, the value of this perk declines since survivors are more preoccupied (being chased, hooked/dead, going for saves, destroying hex totems, etc.). That is, the likelihood of having 2+ people on a single gen as the game progresses becomes less and less. I play killer a fair bit and try to get Iridescent I on both sides. I'm not a terrific killer, but I can usually get a 4K every match because killers have far more pressure than survivors do. The only time I feel the pressure as a killer is when survivors are "gen-rushing" which really is the last remaining pressure that survivor have control over. That said, the game actually becomes more interesting and challenging when the pressure is on their side and therefore a nerf in both of these is absolutely not needed.