But it's not a trail of spores going through space, and nothing in the show would lead someone who'd been paying the slightest amount of attention to think that's the case.

The mycelial network is a layer of subspace, which the spore drive allows them to access because the specific fungus they cultivate exists partially in subspace. Stamets makes that clear in "Choose Your Pain".

Subspace is entirely made up facilitate the stories that Trek tells. It was first mentioned in "Mudd's Women", the fourth episode of TOS to be produced. It has since served as a means of instantaneous communication across lightyears, as well as long range imaging vis subspace telescope, such as in "The Nth Degree". The sensors aboard the ships also operate via subspace, allowing them to detect things lightyears away, and detect things ahead of them while travelling faster than light.

And we learned in the TNG episode "Schisms" that subspace can support life, and even has beings living there. Or at least some aspects of subspace do.

The spore drive in based on the real science of mycology, and extrapolated through a Trek lens. Nothing about it requires any sort of special property that has not already been established as existing within older episodes of Trek.

The only one insulting your intelligence is yourself by believing you're not creative enough to figure out how the spore drive fits into the larger world of Trek.