I'll take a stab at why the mycelial network bugs many folks more than warp drive or transporters: it's everywhere. I'm not saying this is actually a problem, just a hunch about how people feel about things, connotation vs denotation and all that jazz. Warp and transporters (and Q and bunches of other tech/wizardry in Trek) can go perhaps anywhere or do crazy things, but warp requires a crystal and some engines and a mechanic, things people can wrap their minds around. It's an engine that works (practically dramatically speaking) like any engine they comprehend, but... faster. Transporters get you from one place to another, and people get being in one place and then being in another and we try not to think too hard about becoming data-streams or code or if we would be clones at the other site, but really what we are thinking about is being in place A and then being in place B. The spore drive, if it was just about using magic mushrooms in a special engine, I think people be like "what? oh, sure, like crystals in the other engine, like we use gas or something. Many of us fundamentally don't know how engines work so just putting something in that makes it go or mediates something that makes it go or somesuch, sure, I get that". But it's not just putting spores into an engine. It's a special connected network that exists everywhere and ties the universe together, not an energetic force like gravity or a mystical force like The Force (old school SW), but more like The Force (new school SW midichlorian style). Something of substance that is everywhere. "Subspace has something to do with warp", says someone paying attention more than the average viewer. So why is mushroom space harder to accept? Because we understand "sub" things. It's a sub-heading, a sub-marine, the sub-conscious, ie- sub-space is some "under" space, "something only some eggheads would understand, but sure, we get it, like gravity we don't see, science stuff". But we don't have mycelial-headings, mycelial-marines, the mycelial-concious. DSC saying "there's mushrooms everywhere and we can travel along them" makes people think less of sci-fi warp tech, and more The Magic School Bus or Honey I Shrunk the Kids, fun but not taking itself seriously in the way Trek does to tell any sort of dramatic story. Not that Trek is deathly serious, nor should it be. Time crystals, which despite the name (they should be called something else and then just called time crystals colloquially so the crew sounds smart and then not pretentious, just like dilithium crystals are basically warp crystals), are easier to swallow as a concept because time is existential, not a physical thing you can touch, like a mushroom.
