Well I mean, what's the point in arguing with someone who clearly never watches United and is instead just judging everything based on preconceived notions about how a player well be. You never heard of darmian before most likely, so you say he's not a fullback or isn't any good. Bayern let go of Schweinsteiger therefore he must be shit and overweight and past it right? Both of those couldn't be more wrong. The truth is, is that Schweinsteiger was a Bayern legend, who always maintained that he wanted to leave them before he was past it as a player so he could have one last challenge somewhere else while he was still a world class player. As he is now. Since he gave them so many years of service, they didn't stand in his way. He wasn't past it at all. He had a tough injury hit season, sure, but ever since he's come back from his injuries he's been brilliant. Runs non-stop every single game, is a great passer of the ball and still the same world class midfielder he's been over the last few years. Then for Darmian, he's been an excellent right back for us so far, and everyone in Serie A was saying how great of a player he is. Having a poor game against an on form Alexis Sanchez doesn't change that. Everyone has off days.
And how is it an obvious truth that Arsenal is better? Where was that quality against Olympiacos, Dinamo Zagreb, Chelsea, Liverpool or West Ham? Where was that quality in the previous 8 games between the two. United never went 9 unbeaten against Arsenal in the league, so Arsenal were simply due a win and a good performance against us. We'll see how they do in game at Old Trafford later on in the season, but I'm quite confident that we'll win. Last season when everyone was saying they're so much better, we picked up 4 points in the league off of them, and completely dominated the game at Old Trafford. Are you just ignoring that?
Or if you want a player by player comparison... Who exactly gets in Uniteds team from Arsenal? Koscielny, Sanchez and one of Ozil/Cazorla for the #10. Nobody else really, if both are fully fit. You can make an argument for Bellerin if you want more of an attacking threat, but Darmian is way ahead of him defensively speaking. The rest, United players dominate that team. 1 bad game between the two doesn't change that at all.