He's not even the best under 6'3 receiver on his own team, that title goes to Hakeem Nicks.
There's nothing wrong with that at all, it's just the way it is. Nicks is a more physical receiver who has better hands than Cruz.
Cruz will never be as physical as Nicks, but he is more versatile. He can line up in a variety of ways, such as on the outside or in the slot.
Cruz and Nicks compliment each other well due to the contrasting styles, but Nicks is still the better receiver at this point in time.
The closest example to Victor Cruz right now is Wes Welker, they're both relatively smaller receivers who make big plays after the catch, but Welker is a better receiver than Cruz at the moment.
I do believe that Cruz has the potential to be a top-five receiver in the NFL, and the same applies to Nicks. However, I don't believe that to be the case at this point in time.
The biggest issue with Cruz is going to be patience. He's already developed at a pretty rapid place, but he's not just going to wake up and be a truly elite receiver.
He still has to work on the dropped balls, even though he has cut down on that as of late. Time will tell with Cruz, we just have to wait and see.