In terms of usability I really find the tab to be way too high, event in their small version. I know it would be more complex to manage, but maybe have the height of the tab be dynamic: 30px as long as it we doesn’t need to scroll and then reduce the height as we add more tab until they are at the minimum that stays clean (maybe 15-20px) and then have the scroll bar appears.
That dynamic height could be expanded to work from the large tab (60px ??) down to their smaller version (15-20px).
The main goal of having vertical tab for me is to see the maximum tabs possible at the same time.