Davis really is a transcendent player. Damn near seven feet with the skill set of a two guard. Much like Durant, the fact that he's never going to be able to put on a ton of weight (relatively speaking), is going to be irrelevant because of what a freak he is. 20 points, 10 boards, 3 blocks...and he doesn't turn 21 for ten days. If he isn't a HOF, it will be because his body broke down.
Drummond is also a freak of nature, but in a different way. He's a 6'11 guy with an amazing pair of hands, superb body control, and super-human athletic ability. Unlike Davis, he will be chiseled with a few more years in the weight room (think of the LeBron/Dwight transformation, he's headed down that same path). The difference between him and Davis is that Drummond didn't grow eight inches his junior year of high school. He still doesn't have much in the way of a post game, he can't really take you off the dribble consistently, he has no jump shot, and he's a major liability from the three throw line. In the case of a normal big, that combination of weaknesses would earn you a ticket to Europe or a job at Home Depot, yet Drummond is dominating NBA games because he's a Herculean specimen. He still probably needs 3 years or so to truly put everything together, but if he ever does get there, he could go down as one of the best of all-time.
LeBron and Durant are basically Ali and Frazier right now, and it seems like they take their games to new, unimaginable heights each night. The dynamic is simply awesome because there seems to be some legitimate one-up-manship going on, and that makes the head-to-head match-ups even more of a spectacle. Drummond and Davis obviously have a long way to go before they can rival even half of that sort of match-up, but given neither has reached 21-years-old, and really, would both be in college in a different era, the Duncan/Shaq comparisons aren't as absurd as they may seem on the surface.