@Vlad I'd like to make another case for the safari style tab groups.
Named Windows in Orion are pretty cool but they are just windows which are temporary, there is no sense of persistence. Yes tab groups don't actually save the state of the tabs but if you click on the red x button (safari) on a window that has a specific tab group opened it will close the window but will keep the tab group! in the named windows implementation (in Orion) if you close a window it's gone (I know you can re open it but that's not the point).
in other words tab group are mental separation of different tabs. Let's say you have a tab group named "shoes" where you have a bunch of open tabs to research a new pair of shoes you want to buy. At some point you want to go back to work and you switch to the "work" tab group. What happens is that "shoes" group it totally hidden, it's not minimised nor is it in still visible, it's basically tucked in until maybe in 3 days you have some free time to continue where you left off. same for the "work" tab group after work you might have some loose ends and you don't wanna loose those tabs but at the same time you don't to be bother by work during your non working hours.
This is also very different from bookmarks also because you maybe a lot of these tabs only matter for a short period of time while you doing the shoes research for example after which they serve no purpose and you can delete the tab group.
finally Safari has this feature where you can take create a tab group out of some tabs. This is important because besides the tab groups you can also just use safari normally but what if you open a fresh safari window start a new research or topic and then decide that you'll pause for now and continue later, all you have to do is to create a new tab group from the currently open tabs, give it a name and bam your progress is saved for later
I hope this use case makes sense