To my knowledge, Barry has always been faster than Superman, no matter what versions they are. I think COIE Barry would be faster than Wally, but Wally is considered the fastest Flash because he has the most consistent speed feats.
As far as I know this has not been made yet. From what I have seen many people agree that Sauron can defeat most other powerful villains from popular franchises such as Voldemort or Darth Vader. Can the most powerful Star Wars character defeat Sauron?
Now that I think about it, I could see them actually deaging Parker back to his teen years, mainly because the MCU's so popular and because most people dislike what Dan Slott's been doing with the character in the past few years.
And yet, they haven't really been pushing the MCU into the comics. They just push whatever character is about to get a film. Steve Rodgers isn't Captain America, Tony Stark's been in a coma for a while, and Jane Foster's been Thor for the past few years. They've haven't really been pushing the MCU in cases like this.
I'd say there is a chance they would deage Parker, but I don't think they will.