Yeah, those are valid excuses for him to be below his best.
I haven't been entirely convinced by him before, though. Even last season when he was generally very good, I wasn't happy with some aspects of his game. Particularly his footwork and apparent reluctance to come of his line. Everyone spent so much time taking the piss out of Joe Hart, it was as though De Gea can do no wrong. Ditto Chesney at Arsenal.
Meanwhile, there's been a whole bunch of games where those two have pulled off a string of top saves and been the difference between winning and losing for their teams. If we're really honest to ourselves, how many games can we think of in the last two seasons where that could describe a performance from De Gea? One? Two? And it's not as though he's not been seeing much of the ball. IMO there's been a worrying amount of games where we've conceded a lot of goals, from relatively few shots at our goal*. And that's not even getting into the lack of organisation throughout our defence.
*Some stats from last season on saves/shots.
Dave doesn't even make the top 10.