It's been one season of a kind that you can't really tell where it'd go. The race for the top four will definitely got to the wire.
You can't really put your money on Arsenal to beat United if you look at antecedents even when United were in their worst run of form. It's a game poised 50-50 and the better team on the day would win.
True, United always use Arsenal to end their bad run just that these players don't have what it takes. Like you said, let the best on the day win.