That's wild, I've seen huge performance regressions from changes to Base, among commands being dropped, irreconcilable breakages with basics of the ecosystem, spurious bugs in the networking libraries that are nearly impossible to chase down, and the menagerie of compatibility with essential packages break. I stopped caring around 1.7 when I realized this was the norm and it wasn't going to change. You must be honed in on some specific packages with a lot of custom code.