Back to my comment that started this: That would be a flat list with no grouping and little to no context. Tree Style Tabs automatically organizes them by context.

For example, one of my root tabs is Youtube. Immediate children include a few channels that upload a lot of videos so I don't subscribe to them (they'd drown out the ones that upload rarely) but want to keep up with them. Those then have child tabs for their videos I want to watch/listen to at some point, but haven't gotten to yet.

I do the same on here, one of my root tabs is the Hacker News homepage. This one has a bunch of additional long-running tabs, interesting projects I want to try out myself, or reminders to try something out and maybe switch to it instead of whatever I'm currently using. Most of these have further subtabs as I've started exploring whatever it was but not yet finished with it.

And yeah, you could do such groupings with bookmarks... but that's manual work. This is automatic.

Both open browser tabs and bookmarks get auto-completed by the omnibar in contemporary browsers. One important difference is, after a new browser session is created, those pervious tabs go away, but the bookmarks stay. The "chaos" bookmark method results in more chaotic omnibar auto-complete suggestions over time. Unfortunately, that seems like a worse outcome.