Thank you for the feedback. The sidebar is indeed oft-discussed. And we don't claim we have all the right answers. We work hard every iteration to make the best decision, ship updates, and get feedback.

This is the issue where we discussed the sidebar change. Feel free to see what contributed to the decision. https://gitlab.com/gitlab-org/gitlab-ce/issues/26200

This is the ongoing issue to discuss the change and any future iterations: https://gitlab.com/gitlab-org/gitlab-ce/issues/29835

We are working hard to improve UX and navigation specifically at GitLab. Our UX team is focused on design and user research. Here's some work on the research end: https://gitlab.com/gitlab-org/ux-research/issues/3.