Or maybe Rafa just doesn't get to the big matches when he's off and Roger does... It's all useless speculation.
And actually Fed is the one who can change his plan when things go wrong. Sometimes he's been clearly stubborn (arrogant?) about it though. Rafa changes attacking patterns, but doesn't really have a proper Plan B ever. That's why you find him looking like a deer in the headlights and seeking eye contact from Uncle Toni when an opponent is blasting away.
Rafa simply has a massive, safe weapon at his disposal that enables him to force opponents to aggression beyond their capabilities. His game is built purely on utilizing his forehand to the max and he's doing it very well. In a risk/reward analysis I would say it is the greatest single weapon tennis has ever seen. Yes, the final shot is mostly in opponent's racket, but stats tell the same story from one match to another so it's all about Rafa. And when an opponent is blasting away, it means higher risk and higher risk means that eventually the level will drop. Sometimes it doesn't in 3 set matches and in rare cases not even in 5 set matches, but usually it does. That, however, has nothing to do with Rafa's choices or changes in-play.
And also skewing the stats is of course the mismatch to one-hander BH's (especially Roger's) so Rafa's stats are slightly inflated by the extensive number of Federer's finals appearances. Yes, he's also good enough to win anyone else, but I'd say the mismatch has given him a few Slam titles vs. Fed. That's not to take anything away from Rafa, just pointing out that few of those times someone who lost to Fed might have been able to push Rafa more due to not having such an obvious "handicap". Shoulda, coulda, woulda... I know
And this, ladies and gentlemen, is exactly why this thread is not going anywhere. If you accept a theoretically unsound system (i.e. works only under certain criteria), then you're always free to move the goalposts.