Arsenal have done as well if not better than Man U in the CL for 2 or 3 seasons before this one - along with most other competitions in fact!
It seems Man U fans are the new Liverpool fans, winning the CL over 6 years ago doesn't change the fact you're struggling to get past the group phase and will probably go out as soon as you reach the knockout stage like you have every season bar one since you won it. And of course this is the first time your group hasn't been the easiest since you won it.