I mean, that's great if you like that (and have a nice wide screen), but not everyone does. I personally just... can't get used to using a sidebar for finding my tabs, and it also isn't as useful in my opinion for CLOSING a bunch of them once they're open. I'll admit though, the tiled previews from tab stacking is super useful and probably the best way to find stuff I've seen with the horizontal bar. Still, if you have a bunch of different tab groups, you still need either scrolling (which doesn't work well with a mouse, for some reason) or to show more of them at once via shrinking... and you can't currently do both at once, or have it transfer as one becomes more useful than the other.
