You're not getting it, aren't you?
It's not about not being able to follow the bare bones of the structure. It's about being able to get the full experience by simply watching it. It's the same with ST09: "Oh, Nero's motivation makes no sense? Well, it's explained in the comic book, you need to read THAT first!". Sorry. I'm not doing that. If your character motivations are shit, and I need to research and buy external material to make sense of them for the thing I'm watching in the first place - yeah, I'm not going to buy that but will complain your character motivations are shit.
Same rules for DIS. Nobody will not get what has happened this episode. It will just come across as really stupid If you're unfamiliar with these specific old episodes.
Earlier you said you have to know what happened in the mirror universe Enterprise episodes to understand this episode. I'm watching Discovery with my wife who has not watched any other Star Trek in her life and she knew what was going on and was not confused. The fact that there is a ship that previously went to the mirror universe without the spore drive is all a person needs to know. The extra details around that ship are superfluous to the story and only adds colour to us Trekkies who have seen every minute of the franchise.