Indeed it’s really a sisyphean task. Which is why I came to the same conclusion you did: Stationary skylight offers the best compromise. Baking light isnt fun but at least all thats required is pushing a button and waiting.
Only thing I would add is that I think the least problematic way to manage this with a movable skylight is to just design your level with S-bends between exteriors/interiors to hide skylight intensity transitions (which you mentioned in your post) and use “opaque” emissive dirty windows with fake interior/exteriors where necessary. In both cases you solve the problem by simply making it impossible to see inside/outside at the same time. Lots of games already do this just so they can hide large sections of the level when the player isn’t in the space.
Understandably though it’s not something any designer likes.
Supposedly Epic is targeting 60 fps on next gen consoles for Lumen and scalability is a big focus of UE5. I’m really hoping Lumen is scalable to a point where you can sacrifice the indirect lighting and use it only for skylight occlusion to get it to run better on old hardware. Otherwise I expect we’ll be doing more of the same for a few more years at least.