I don't know about that. When I mention Shawn to marks and casual fans that were around during his prime (specifically 95 and early to mid 96), they tend to remember his personality and on-screen character above anything else. One of my favorite things about HBK was his ability to get his character across to fans either through promos or ring work.
As far as mic skills...I dunno. It really all depends on how you look at it. I'd give storytelling to Bret, but in terms of getting his character over and in entertainment value I'd give the edge to Shawn (keep in mind that I'm talking about pre-comeback Shawn...damn near all of the promos he's cut since returning have been weak). Bret's a lot better than people give him credit for, but to me his promos seem kind of generic when compared to Shawn. Shawn's got a distinct style that makes his personality shine through and stand out, and that's something you really can't say about Bret's mic work.