As a consultant, switching between my many clients, testing, and home accounts is simply Alt+F+B+Arrow down ("Open new container tab"), all within the same UI, in the same window, with colored tabs, with the same extensions, and same password manager.
I've been in situations needing up to half a dozen different Microsoft accounts (multiple Teams clients in Firefox, for instance), other browsers haven't solved this daily use-case for me.
"Shared everything", is exactly what's undesirable about container tabs and what makes them a non-starter. I'd like to keep work actually separate. I don't need work tabs, or work history, or work downloads polluting the "main" profile. I don't need work extensions to be active outside of work. (there's just no way to make some extensions to work with just specific containers, so that's a dud.) All of that stuff can be in it's own space, and it would also make switching a bit easier - open profile, resume tabs, close profile, things stay put and ready to pick up where you left off, without needing to juggle tabs within the same profile and having them be an eyesore, be it work stuff on a regular profile or vice versa.
I've been in situations needing up to half a dozen different Microsoft accounts (multiple Teams clients in Firefox, for instance), other browsers haven't solved this daily use-case for me.
It's an easier account management tool.