Like you said, they are exceptions to the rule. Barkley is listed as 6'6, but Barkley was a "heavy guy" in the way he played. And 6'6 isn't too small for a PF. If you look around in the NBA you won't find many, but there are guys like Jason Maxiell that play a lot of undersized minutes.
Second thing, I'm not complaining. I really like this game, and as far as I understand these guys are trying to create a thing as close to reality as possible, so I don't see why I shouldn't participate in discussions and give suggestions. I'm not saying everything I argue is absolutely right, I'm open to arguing and agreeing on the best solution.
All the examples you give are correct. Dirk Nowitzki is a great shooter but he's not a ball handler. There's nothing wrong with big men who can shoot, in the NBA lots of PF's come out to shoot the 3-ball. LeBron, Magic, Durant are 6'8, 6'9 which I still find reasonable and are exceptional players (Durant's not there yet, but he'll get there I think). But tell me if you have ever seen a 7-foot point guard.
My point is, an exceptional player can play everywhere on the court, but there are no average 6'4 Centers or 6'10 PG's, let alone 5'11 C's and 7'1 PG's