I have read better fanfic than this for sure. I have even read better fanfic where MJ was married to another person. It's....not good.
The kids, rabin's death, Peter not reacting to MJ's powers, the clumsily added two pages of flashback. So many little signs in 26 that this is just a badly done mess. Truly Awful. It's my 3rd worst Spider-Man story of all time at this point for a reason.
Regarding sales, I did the math ten years ago while arguing with Slott and there was a definite and significant dip right after OMD. There's no question it cost them a big chunk of readers, though it's been too long and they purged these boards so I couldn't tell you how many. In my memory it was like 30% or something like that. Significant. But not that surprising considering they had just published the worst story in Spider-Man history.
AS for performance yeah it's kind of a mixed bag. There's definitely a value in that consistency and giving each writer time. And there's also some value in the old books of just having different storylines going at the same time. He's fighting Rhino in Amazing but Mysterio is Spectacular. At the same time, perhaps because I'm impatient, I'm very happy for the main story to churn so fast now. During the Spencer run when it was good It was this nice treat every couple of weeks when I was running my errands. I'd go to the comic shop, pick up everything, then go have lunch and read everything while I ate. And it was great getting to push the story forward twice a month instead of once. But you do make sacrifices. You have to have rotating artists and that can lead to dips in quality. The writer probably needs a break every now and then. Honestly, BND and its rotating team wasn't a bad idea either, they just...only had one actually good writer.