"Delubrum Reginae is soloable"

[Coletergeist]

No. There is zero scaling under a certain player number based on my experiences. It likely scales to a minimum number (maybe around 10), but lower than that and it just becomes effectively undoable. The damage we were doing in my attempt today, even with lost actions, was almost nonexistent.

Ah, well...
I wouldn't say undoable, more difficult probably, but not undoable. Lost actions would make it easier, but you're allergic to those.

Even if we did clear it it would likely take an obscene amount of time.

I mean, if you want to get it done, just take the time to do it and get it out of the way, even if it takes the entire time allowed in there.