PAD explained it like this when he brought him back... how entertaining would it be to watch Flash go through months of painstakingly tedious physical therepy?
I actually would have liked to see that, It would have shown that being in Peter's life has lasting, sometimes negative consequences.
Having Peter be affected by watching one of his best friends on a painful road to recovery due to an injury indirectly caused by Spider-Man would be alot more interesting to me than. "I'm all better now!" and "By the way the meaningful friendship we forged over the years and had.... well I forgot about it. No character development for me!"
Having Flash being somewhat disabled (Needing a cane, or some other physical or mental injury) and still be friends with Peter would be constant reminder to Peter that everyone he touches is at risk, and not everyone comes back as good as new like him after a conflict.
Flash IS disabled. He has a brain injury. Alot of people with brain injuries have significantly altered personalities and memory loss after. It's not regression of his character, but brain damage. You're taking a very cynical approach to an actually somewhat realistic depiction of someone who's had a grave brain injury.
But physical therepy? How many times could they show him learning to walk and speak and eat and go to the bathroom? Even Hobie Brown recovered from being a quadraplegic in the span of one arc.
And actually, Flash may not be as intelligent as he used to be (going into a brick wall at 70 mph will do that) but he and Pete are fine. He even let Peter stay at his apartment.
