imo GitHub has to be up there. I think some of the recent changes to search and making the code view more IDE-like are steps backward from a “polish” perspective, but still useful features
Like, nobody, including the original issue author is actually enthusiastic about the fix. It’s just one less papercut.
I’m sure if these things were actually seen by devs they’d add a two line change to a random PR and it would be done in a few minutes.
You might get amazing UX mocks and wireframes and designs etc from the UX team, and the mockups from Figma or whatever may have user-tested really well, but if there is huge latency in the real implementation then that is a usability-killer IMO, regardless of how polished the UI is.