If McCarron would have had 1st round worthy high end skill he would have been a top 5 or even top 3 pick in 2013. Remember, we had the 25th overall pick in a so so draft.
As for the other guys you mentioned, I liked Erne but I heard rumours he didn't want to play in Canada and the other 2 aren't exactly sure fire shots to make the NHL, let alone in a top 6 role, or at least I don't think so. Zykov in particular I think was the 7th ranked NA prospect overall in the draft, and he fell like a stone. Plus we could have had him with our first pick in the second round, so its obvious Timmins and Bergevin didn't want him. Personally, I'm not crazy about drafting Russians in general, although I certainly believe Scherbak was a good pick for us where we took him (I know that probably doesn't make sense). There's also always the possibility that the habs brass thought someone else was hot for McCarron and would have scooped him up before they got to pick again, who knows.
I don't really blame you and others at all for not liking the McCarron pick, I remember when watching the draft on TSN when they did their rankings out of 5 for all the players chosen for skating, puckhandling, compete level, hockey sense, and shooting and while everyone else who went before him had 4's, 5's, and a few 3's McCarron was all 3's with a 2 and a 1 I believe. All I could do was shake my head but Timmins liked him and the guy had size and a lot of what I read about him afterwards said he had good hands, was very raw in potential, and most importantly played a style that made the opposition uncomfortable. I think those who have pointed out that guys who are pure skill without much else to offer pidgeon hole themselves into a situation where for them to make it its either top 6 or bust. As for the size AND skill argument, let me tell you bud everybody wants that kind of a player. They are hard to get. Hell even big goalies are the norm now.
Anyway, I hope this better allows you to wrap your head around my thinking about this whole thing. Cheers...