Maia right now I wouldn't consider a 1D BJJ guy, but I would when Anderson fought him, as well as being undersized.
Alves is more of a jack of all trades but at the time was pretty feared, he was 10-1 prior to GSP just beating solid wrestlers Hughes and Kos. At least as good as someone like Okami comparatively. Hardy I didn't mention, I agree he's 1D and had zero chance against GSP. Serra I didn't mention.
Hughes is absolutely not 1D, having a very good ground game. Shields also. Fitch also.
I'm not grasping at straws I'm just suggesting that Anderson's run was favoured by having minimal other guys in the division at the time that were lesser likely able to expose his weaknesses, or do anything with them. The demographics suited his style.
If he was instead fed a steady diet of say, middleweight versions of Shields, Hughes, Kos, Fitch, Hendricks, etc. then perhaps he would have not had the success he had. That's all I'm saying.