Wasn't Danny trained at K'un L'un from when he was relatively young? Like, adolescent/high school-age? If so, he'd be more experienced than Peter, since Peter only got bitten when he was 15 and Danny's probably 5 or more years older than Pete.
As for Peter's strength, I think it's pretty much assumed that Peter always pulls his punches. He fights mostly bank robbers and normal humans, and if the writer is writing him correctly, he'd be absolutely mortified if he accidentally killed someone, so he plays it really, really safe and pulls his punches back to basically a really strong but normal person. At least, that's how I rationalize his utterly *****-like strength lately, in spite of all his recent upgrades.
I think you may be onto something with the overconfidence angle, Kitsune. Tony has gotten overconfident, and that may be the way Peter manages to outdo him in the upcoming arc. I don't really have anything against Peter beating Tony, it just seems very unlikely given all of Tony's advantages. It'd take some pretty crafty writing to make it plausible without being too convenient or making Tony himself look bad. He's not exactly easy to outsmart, after all, even if Peter is known for outsmarting foes.
