I think I'm overall in favor of the UI option in the pic here. A small, non-intrusive prompt that can be easily skipped. For the most part, when you take damage, you're thinking "Oh shoot, what can I do now?" and so I don't think a minor break in the action would be that sluggish. And hitting spacebar isn't super time consuming. The Solasta pop-ups have a lot of info on them that take up the screen space and can be overwhelming to read if you aren't aware of your options.
In a way, it actually gives players more "turns" during the round. Take multiplayer for instance. Instead of having to wait for every other player and every enemy to take a turn, you get another moment to be part of the action (if you choose).