Again, I don't know what the issue is, if there even is an issue. I was purely speculating based on how I understand the business and what the things are that I understand will hold someone back. It could be charisma like you said, I don't know. Based on what I've seen from him in interviews he doesn't appear to be a naturally charismatic person so that could be it.
There are two other examples of guys like him that I can remember entering the WWE (WWF at the time) and those are Kurt Angle and Mark Henry. When they first came in they were immediately given a push. Gable has not. Historically those kinds of guys are not put on a shelf once they are introduced. However, things are very different now than they were in the 90's.