I see your point now, I was preferring containers because I have this scenario where I want the data separation it provides without the need of reinstalling add-ons, especially on a temporal container/profile. The shared window can be nice on some particular moments where I don't need to have a lot of pages opened and are continuously changing from tab to tab.

Thinking over about you said, now I think I like things from the two worlds, maybe better interface to containers or even better UI for profiles, with options to overcome the containers (maybe should be better for the average user instead of having both).

For the time being, I prefer to have both options (don't have it now) but I think both can be improved.