jason cant hurt colossus, he doesnt have the strength to do so, colossus beats him on strength speed and intelligence. its not just that hes better at these, its that hes so far ahead of jason in each respect. regeneration is no good if youve been decapitated. jason lacks the ability to do damage to colossus, colossus can tear jason to pieces.
well, jason has had the vast majority of his body blown up (before being upgraded into X), and he has been able to regenerate and kill people within the same film, so even though collossus would most likely win temporarily, jason can win in the long run. Plus, all he has to do is catch pete without being "armored up", and a simple slash of the machette will do him in.
taking into account that colossus armors up almost instantly, i think if he suspected someone was chasing him he'd be armored already. sure if jason caught him unawares maybe, but how likely is that? the only reason jason was upgraded and put back toghether was that damn ship, yes he can regenerate but can he regrow his head? there is no long term because five minutes after this fight starts itll be over, for the simple fact that colossus is so durable jason hasnt got a chance of denting colossus' skin.
no man he did it in another jason movie too, after he got blown up by the fbi.....umm I think with the armor and strength upgrades from the ship jason x wouldn't be the walk in the park everyone's making him out to be but collosus is gonna put the hurt on him pretty badly nontheless. (off topic, but I would like to see jason vs. wolverine I think their fighting styles/abilities match up pretty nicely)