I especially find that bit with the spore energy extractor in the mirror universe that could kill all life in the multiverse if not stopped jarring, because, if you have a potentially limitlessness number of alternative timelines, and the massive expanse of space, to develop that tech in, the odds that nobody else ever built one of these drops to essentially zero, except that the existence of the plot at all implies nobody else ever has.

Agreed. It’d have been perfectly fine to scale it down to have the extractor messing up the nearby mycelial network/subspace enough that the spore hub drive would become inoperable, and they’d lose the only method they had to get home.

If anything, that might be more compelling, since you could easily squeeze in a character conflict with some people wanting to leave, damn the consequences, or make preparations for a long term stay in the mirror universe if they got stuck.

In some way, its probably similar to Lazarus’ machine. He managed to build something capable of obliterating two universes. It didn’t seem that difficult, or that much more advanced than the Enterprise, you’d think someone else would have built something similar, and accidentally destroyed the universe in so doing.