I agree a lot. Had Vista and XP machines in the past.
Then mainly used Win10 and KDE Plasma was a solid upgrade.
But they really copied the Win10 look which is atrocious. I agree that WinXP and 7 and the era where way better.
There are themes for everything though. Its just theming. I dont know if all apps support it and have never dealt with it, as Breeze works pretty well with Adwaita and Electron apps too.