I use multiple windows specifically because I want different tabs in them. With this "feature", we have the clutter of all tabs in all windows which makes it harder to find the one you're looking for. Screen sharing can leak tabs you didn't mean to show during presentations; videos playing on another screen would switch screens as you try to find the right tab; and those of us who never cared about workspaces were forced to use them.

But again, the main issue is this was an extremely opinionated change that forces people to change their workflow and was pushed to all users with no way to disable it. I had been using Zen for almost a year at that point, and, what was supposed to be a minor update made it extremely frustrating to use.