I really like the thing about containers that they can be mixed in a window.

Personally I think both options should be possible. Choice is good

There are definite advantages to this over containers in some cases, and definite advantages of containers over this in others. Containers are always hard to manage with multiple Google accounts if you want one to be default, for example, because of the way they do accounts and how they redirects everything work. Any time I'm in "workspace" type window, I want Google to just load in that container, so a profile would be great.

For other things, I really want containers. For example, if I'm prompted to load my banking side from a google email, why yes, I do want to open this tab in my baanking container, thanak you for asking, Firefox. Oh, this is a link to social media? Please cordon that off to a separate container as well.

Profiles are good, containers are good, they both serve slightly different use cases and can be used well by the same person, so both should be first class.

In FF, I have an email window with different tabs for each email account. It would be a nightmare to switch through multiple windows to see all of my email.

Should be easy enough to accomplish with an extension. Maybe one exists already.