That is true, I share a similar issue when out of form (i.e. with bringing long range aerial balls down) but then again we have always said Rooney isn't the norm in the elite professional realm. How many top class players outside of Rooney, really lose their first touch to the extent he does (Suarez can sometimes be inconsistent with his touch I guess) and to be fair when Wayne was a kid, his first touch was on another level to a Rashford.. he had some brilliant first touches, where he'd spin into space even with someone up his arse. I personally think it is when the drinking and his physical side wasn't where it should be, his first touch and reactions began to suffer with it.
When he is fit, and I mean he looks physically sharp.. his first touch is usually pretty good. This season after the wedding debacle, when he has played with a point to prove, his touch has been okay. End of the day, for all the criticism Wayne gets, he is a very natural footballer.. you just know he's got a good footballing brain, he's had that since he was a kid. Rashford sometimes looks like a Walcott, all speed and no nous.. yet in other games, he looks like he has an astute understanding of the game.
As a number 9, you can't really afford to have on and off days with your first touch and certainly not if you want to play for United. Lukaku is a player who I can think of that has a terrible first touch, lacks consistency with it and it has held him back from being a top top tier striker.. hence why he is at Everton. Far too early to say that about Rashford, as he may be going through second season syndrome, maybe even an undetected growth spurt etc etc.. but in the long term, his first touch and technical ability in general can't be hit and miss. It needs to be reliable, so that even if he himself has a poor game from a goal-scoring perspective, he is still able to function as a focal point for the attack and bring others into play.
Once his physique fills out, he can use that to protect the ball better.