(Before I get you-can-do-this-and-that replies, I know Profile Manager exists, and that's an ugly hack: macOS users should not need to run multiple copies of the same app bundle.)
The big thing that's different with container tabs is that after you set it up (which is done little by little as you decide to open something in a specific tab and then mark it to always open there), it's not something you actively manage, it passively does what you want. That's why it's so different.
Having every site be it's own container (which is also a mode Firefox supports, to my knowledge) would be slightly more passive, but also likely cause problems with some sites that use multiple domains, so I think container tabs is a good compromise (for now) that allows good compartmentalization while also allowing escape hatches for sires that require it.