I assume the “kill it” comment was a little tongue-in-cheek. On small SBCs, like a Pi, or old hardware, it could be a problem. I’ve seen people with flatpaks taking up 30GB of space, which is significant. I’m not sure how much RAM it wastes. I assume running 6 different applications that have loaded 6 different versions of Qt libraries would also use significantly more RAM than just loading the system’s shared Qt libraries once.
Yeah, I agree. I do use Flatpaks, Snaps, and Appimages sometimes if I can’t find a suitable deb repo/package. Flatpak is the best out of the three because they do try to avoid too much duplication through runtimes. I also use Docker quite a bit, which has similar issues (and benefits).