Following habits of working in most applications, I believe most users have the least of cognitive load if they reach for common tasks upwards, instead of downwards. This includes preview sizing, undo/redo, and everything else currently placed at the bottom-right.
On the other hand, the natural area to reach for these tools is occupied by tabs, which are not relevant for current document editing and far less used. Also, if the speed of switching between tabs doesn’t get resolved, personally I will hardly use them anyway.
For this reason, I would love to see an additional preference to switch the position of the Breadcrumbs & Toolbar and Tabs.
Thanks!