Drew Brees played 15 pounds heavier than young. Young was also behind the Alabama line throwing to Alabama receivers. He's not going to have that talent advantage any more. I think if he can stay healthy, he'll be good but that's a huge caveat.
the article noted that Young's OL wasn't all that great nor were his receiving corps. It's a huge risk to take him at #1, but it's not out of the question that he succeeds (and bulks up a bit).