I just think expecting it to never be discovered again over 900 years is a little hard to buy. Sure, not having it by TNG works for me, but the fact that this whole mycelial network crosses the galaxy and multiple universes and was never discovered again, even almost a millennium later… I don’t know.
A good example- we have no idea what ‘Greek Fire,’ a secret military technology used by the Byzantines actually was, but we have many ways to recreate what it did through rediscovery of technology.
That said, I realize it’s just a TV show. I take your point about it being in the Prime timeline. I just wish there was more reconciliation with the rest of it, like why the Klingons look totally different in Discovery than in SNW and Picard. You can just dismiss that as being the same as the Klingons looking different between TOS and TNG with no explanation (unless you accept the explanation in Enterprise that many people hate), but I still would have appreciated an explanation. For example, I saw it suggested that the Klingon empire was actually more diverse than it seemed and various ‘types’ of Klingons were in power at various times. So in the TOS era, the “human” Klingons were in charge, in Discovery, the Discovery Klingons were in charge, and in TNG, the TNG Klingons were in charge.
So the “impossibility” of the spore drive doesn’t bother me. I just have a hard time with the idea that it was never rediscovered by someone else over many centuries. One solution would have been that everyone was using the spore drive in the future until the planet that the Kaminar guy was on made it impossible instead. It could even have ended differently with the mycelial network becoming unusable, even destroyed, and them having to go back to, maybe even re-engineer ships with warp drive technology. I also suggested above that they could have had Control use a weapon that destroyed the network and it took 900 years to heal. I can just see so many ways around the problem that they could have used but didn’t. I don’t want to suggest I’m a better writer than they are or anything, Discovery has had some episodes with exceptional writing, I just think this particular story element was handled badly in this specific case.