Yeah I hate the term "sideload", but I'm guessing they meant it in the sense that they installed a separate DE within a distro designed around its original DE. Ideally, the DE that ships with a distro should be able to solve problems like video streaming and KiCAD with relative ease in the year 2026. Although I'd be curious as to why exactly that person decided they needed to change their setup in that way, I also can't say I'm entirely surprised that they would end up needing to do something like that.
The idea of a distro being "designed" around a particular DE has always annoyed me too. I'd hear people saying they wanted to try KDE so they wiped Ubuntu and installed Kubuntu instead and it's like, buddy you could have just... installed KDE. I know some specialized distros are really all about shipping a nicely-configured setup for their specific DE, but your old standbys like Debian, Redhat, Arch, Slackware, these are all infinitely flexible.