Pain Res should be made partially base kit
Since the beginning of time, gen slowdown has been meta and killer builds have been heavily limited due to the necessity of running gen slowdown. I think the next step to revolutionizing killer game play is to improve the base kit gen slowdown to point where you only need 1 gen slowdown perk and more is optional. This will greatly open up the perk options for killers and allow killers to run something that isn't a full gen slowdown build. According to Nightlight, the most used perks are all gen slowdown and aura perks.
Pain Res is a good option to make base kit since it's by far the most popular perk sitting at 32.5% usage. It also rewards killer for not tunneling, so it doubles as an anti-tunnel incentive. Borrowed Time was once made base kit, so I don't see why Pain Res can't be made base kit too.
The gen slowdown perks would need to be tuned down to account for killer having better base kit slowdown, but I really only see Pain Res and Pop needing nerfs. The other gen slowdown perks are already balanced.

Comments
Can we have Windows of Opportunity partly Basekit as well? You know, because it is the most used Survivor Perk.
Furthermore, Pain Res does not do anything to incentive not to tunnel, it is still always the best to tunnel one person out and then get the rest of your Pain Res-Stacks on the three other BP-Pinatas you have left.
Borrowed Time was mainly made Basekit because it is stupid Perk Design that you have to rely on someone else having a specific Perk when they farm you. Something you cannot control.
IMO Pain Res is way beyond good enough as a Perk to invest a Perk Slot in and there is not really a need to make it Basekit. You have a strong Perk, use that strong Perk. It is a good investment.
Honestly, it should be base kit. This would lessen the gap between survivors still learning the game and veterans, which would lead to better balancing. Currently, the game is being balanced based on most survivors running WOO and missing a perk slot.
That's false. Tunneling has become much weaker with DS and DH being meta perks on strong teams. At best, you'll get a 2k if your strategy is to hard tunnel a strong team. The new killer meta is to run all these strong "hook every survivor" perks, so that tunneling is optional. In particular, Pain Res + DMS + Grim Embrace + No Way Out on most killers.
Off The Record exists now, so it's something you can control.
I don't think you read the post. Most gen slowdown perks are strong perks that are good to run, which is why that's pretty much all that's ran. The point of improving base kit gen slowdown is so gen slowdown perks become more optional and perk diversity improves for killer.
I agree that killers need some basekit help. I'm not sure how basekit Pain Res would affect the game, but it doesn't seem like a bad idea. Especially if BHVR would make it so Pain res doesn't make you let go off a gen.
Some things that would help with consistency, in my opinion:
I feel like, once these basekit start-of-the-match mechanics have been covered, it will be much easier to balance the game. Maybe even basekit Pain Res then.