You are being harsh.
I agree with your post above and he should be a squad player
My problem is you know what you are going to get....very little, so how would you use him? he isnt an impact player because he has no impact, he isnt strong enough to use as a wall like fellaini gets used for.
If you play him against weaker sides you run the risk of not having an attacking threat on which ever wing he plays on and may end up with a 0-0
So his only use is when we are already a head and comfortable, those games are few and far between.
Atleast with depay you havent a clue what will happen, he hasnt had the chances lingard has had, Lingards one advantage is for all he is useless, he does keep it simple so wont look as bad as Depay who may try something, certainly like to see
Depay given some time but only because he cant be any worse.