Austin used friends in high places and not wrestling (or fighting, in the case of that match) talent.
In an actual match, your mentality is as much a part of your makeup as your ability to do a Saito Suplex. If you lose a match because you showboat that is absolutely down to you. It's your own flaw as a wrestler, and as a competitor, costing you.
If in basketball a team had a match won and then started doing silly under-the-leg passes or whatever, and then the opposition stole the ball and scored a bunch of times, that is the fault of the team for choking away their lead and not having the necessary mentality to see the match through.
Basically:
Getting outside interference is not an issue of wrestling talent.
Showboating when you "had the match won" is absolutely an issue of wrestling talent.
And besides you can't even say Cena had that match won. If Rock was able to get up and still deliver a Rock Bottom that indicates there was a lot left in the tank. Cena was pinned by that Rock Bottom, too, so it's not like he had much more left in the tank than Rock did (if anything at all).
He could even have been playing possum to lure Cena into the mistake! I mean you might think that's unlikely, but it's as valid an explanation as any.
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"I wish I was French." - blindhobo13
"I don't think you know what "French" means." - As I Desire