Tab groups are there, sync of them too, keyboard operation too, sharing as well (your improved sharing does only seem to work when both the sender and receiver have your browser, so for a niche tool, it probably won't be useful that often).
Which would mean, based on your landing page, that I'd be paying 15$ per month for split-screen.
Don't get me wrong, I think innovating on the browser and trying to find new paths, different to those that have been treaded for years is great! 15$/mo is also ok for a big value-add. But I don't see much innovation here that's not also in the status quo.
Please show me what I'm missing though, as I probably don't have the full picture.