I was trying to compile kwin and it was impossible to read the output because
clang complains if it should override and it doesn't
Something similar was done to Plasma as well.
A warning which breaks the warning output of legacy code (and that's what KWin is) is completely useless. Yes override is cool and useful. And KWin uses it in new code. But adjusting the old code - no that just makes the git history a mess. Nobody touches that code, nobody will change it.