Some people have this crazy idea that he deserves credit for WWE's success back then

lolno.
He wasn't the only one there, I suppose.

He did come up with a lot storylines and ideas for WWF at the time. With Russo I will always say at least he always made sure everyone had a character and had a reason to be on TV. With Russo's ideas you needed a filter with Vince. Russo could throw 20 ideas at the wall. Vince would pick the 5 best and usually use two of them.

Russo is the type of guy who can spit out dozens if ideas with relative ease, but he has no idea which ideas are good and which ones suck. Like Bull said, with McMahon there to pick the gold out of the shit, WWE was able to prosper thanks in part to Russo's contributions. However, in TNA he had no such filter, which resulted in a lot of nonsense booking. If Russo was the creative genius some credit him as, TNA would have been at least close to becoming competition for WWE instead of the punchline to so many jokes.

He was part of the reason, not THE reason.

Man the week after Russo left WWF's ratings went up. Not down like he told WCW they would