Given Vrabel has yet to play a single snap, except, sort of, in practice, I suppose the most direct route to an answer is to say, "It's Drake, of course."
I taught a philosophy course for years. Most discussions, often unfortunately, come down to a seeming dilemma, to an A or B choice that leads to, "Well, which is really more essential, A or B." In politics, for example, this often often comes down to, "Which is more important, Freedom or Equality." Sound familiar? ("Liberté, Égalité, Fraternité" my ass: make up your mind." We hear that sort of thing a lot these days. Accusations of fascism or Maoism then ensue.) When that would happen in a discussion, I would sometimes point out that this might like saying, "Well, I propose to make a little salt for myself, and I understand that I need both sodium and chlorine to get that done. Which, though, is more essential, the sodium or the chlorine?" Either answer, without a lot of fancy footwork of an evasive sort, is wrong.
So they're both essential - liberty and equlity, Drake and Vrabel - to our success, let's say, and perhaps just as there are no degrees of perfection, so there are no degrees of essentiality.
This is all well and good, but I'm not sure it entirely applies. Maybe it is more like, "I propose to make lasagna, but I don't have any basil: I always use basil whern I make lasagna." Hopefully some wise and pragamatic soul will come along and say, "Use oregano."
Maybe the question outght ot be which of the two, Drake or Vrabel, is more easily replaced in such a way that the success and progress can continue? The answer, obviously, I think, is Vrabel.
I would have a slightly harder time answering the question if the choice were between Vrabel and Josh. Preliminarily, I suspect that would be a contest in which Vrabel, as superior a HC as he is, would also come out on the short end.
They used to pay me to say this sort of stuff. What a world.