How about we all stop being wrong, and just try to put our feelings towards the club to one side for a second? How about we judge a player based on what he's proven against a decent level of opposition (not the reserves) in decent competitions and until they do so, we try to keep calm?
There are some players who have so much potential in their position, and already have certain abilities to a high level which means you can easily see how good they are going to be just given time and experience. The likes of Rafael when he first got a game.
Welbeck isnt one of those. And we're still waiting for him to prove himself at a good level.
He had 5 league matches for us last season according to wiki. He scored once. He's had 8 matches for Sunderland and he's yet to score.
Now he'll come good and score goals in the premier league, I dont think there's any reason to fear that he cant hack it in the top flight. Its just there's nothing to suggest he's going to be above mid-table premier league level for the next however many years. Even if thats the case, he could still go on to be good enough for a top club in his peak years because some players just develop that way.
But if he does take that long to develop, he's not going to make much progress at United and will find another club where he can play football regularly. And it may take that step in his career to come good and reach that top club level.
As a striker you really do need to be hitting the back of the net fairly regularly if you're going to make it at a top club. If he moved onto the wing fulltime it might suit his abilities a bit more