Let me put it this way: There would be no problem if they "just" used to get into a subspace realm for fast travel. Those are theoretically unlikely, but not impossible, and we have plenty of them seen in Star Trek. The problem is, was, and for DIS always has been -the mushroom network-. The way they portray it, it's one entire, giant funghi spannung our whole galaxy. That is simply impossible. Even in the world of Star Trek.
Oh, the fluid realm of Specie 8472: That was an entirely different universe. Like the mirror universe, or the Kelvin-universe. Those are okay and spawn from Hawkins (now withdrawn) postulation of alternate realities. But the funghi isn't an alternate reality: It's in the subspace of our one. It is simply impossible to have such a large scale organism spanning our galaxy. Both physically (were would it's energy come from? How the fuck did it ever evolve?), as well as logcially (so, Tardigrades can travel on it. An ability they must have learned in billions of years of evolution - And NONE ever came to Earth? what?), as well as canon (so, like, there has been an exchange of biological organisms for the entirety of human existence with aliens, and that was never mentioned?).
Again: This thing theoretically could work, in it's own fictional universe. Much like the Flash Gordon universe, where there is breathable air between planets, or the Star Wars universe which has the Force in it, or the Lord of the Rings universe, were magic exists, or the JJ Abrams universe, were star systems are so close you can see planets from the surface of different planets orbiting a different sun (Force Awakens, destruction of Vulcan). But this is not the universe Star Trek had created, in the Star Trek universe the year 2017 looks like OUR universe in 2017, NOT a magical realm with Orcs, Demons and space shrooms in it, and as such it sticks out like a sore thumb.
Oh, the fluid realm of Specie 8472: That was an entirely different universe. Like the mirror universe, or the Kelvin-universe. Those are okay and spawn from Hawkins (now withdrawn) postulation of alternate realities. But the funghi isn't an alternate reality: It's in the subspace of our one. It is simply impossible to have such a large scale organism spanning our galaxy. Both physically (were would it's energy come from? How the fuck did it ever evolve?), as well as logcially (so, Tardigrades can travel on it. An ability they must have learned in billions of years of evolution - And NONE ever came to Earth? what?), as well as canon (so, like, there has been an exchange of biological organisms for the entirety of human existence with aliens, and that was never mentioned?).
Again: This thing theoretically could work, in it's own fictional universe. Much like the Flash Gordon universe, where there is breathable air between planets, or the Star Wars universe which has the Force in it, or the Lord of the Rings universe, were magic exists, or the JJ Abrams universe, were star systems are so close you can see planets from the surface of different planets orbiting a different sun (Force Awakens, destruction of Vulcan). But this is not the universe Star Trek had created, in the Star Trek universe the year 2017 looks like OUR universe in 2017, NOT a magical realm with Orcs, Demons and space shrooms in it, and as such it sticks out like a sore thumb.