You definitely don't need containers to "run something that needs a different dependency", it's a massive waste of time and resources and just not what containers were made for. There are/were a thousand other solutions for this, from Nix to chroot to building from source to LD_LIBRARY_PATH to AppImage.

Containers were initially sold as a "security boundary" of sorts. The ability to run some software with the peace of mind that it won't ruin your OS or leak all your data if it's vulnerable. It's the entire point, but it turns out to be extremely difficult to get right. We managed to make a boundary against accidentally messing something up, not against targeted attacks.