I dunno, Office is C++ and yet moving Office 2016 _windows_ around is comically slow and nukes the CPU from orbit. Microsoft - anyone really - has no issues at all writing slow, garbage UIs in any language or framework.
People hate X11 and apps that use older toolkits but I can move Windows around my under powered PinePhone in real time all day long on Fluxbox.
Yeah, this never worked well in windows (I remember switching 'show window content while moving' to 'off' whenever 'on' became the default).
Taskbar 'autohide' is still a clusterfuck (I don't remember a version of Windows, where this feature didn't have at least visual bugs). New centered taskbar in Windows 11 is just bad usability (only smart thing about start button was, that it was in a corner of a screen thereby making it easy to hit with a rough mouse movement).