I’m trying to tinker with my system and replace a perfectly good and well optimized default kernel for some kernel made for specific niche use cases and I don’t see any performance increase. Why would it be?

Yes, surprisingly the default kernel is optimized well rather than just being a badly written placeholder that users should manually replace for their system to become usable.

It’s 2025 and stuff is designed to just work out of the box.

But it’s used in PES (Passenger Entertainment Systems) at least.