Never used command line for profiles, I'd just go type "about:profiles" > "Launch profile in new browser".

This opens a new window with that profile, but you can switch between each window at will.

The lack of discoverability of that "about:profiles" page is indeed a UX issue compared to chrome, but other that that it works pretty well.

For most use cases, I find the more lightweight multi-account-containers more useful though.

Yes and from within the browser about:profiles

And you can edit the shortcut to ask you which profile you want to use when you start Firefox.

You can create .desktop files (or the equivalent in other OSs) for the profiles to open them like normal apps.