Just some food for thought - I have done alot of striking arts [Boxing and Muay Thai mostly] and have only really started to get into grappling work, and I know for a fact, that in a stand up fight, I can knock some of the BJJ guys out with absolutely minimal effort, but let a fight go to the ground, and I'm getting arm-barred, or triangled, or just plain choked out [I remember my first take down attemps, absolutely laughable]. Flip side, a buddy of mine has done BJJ, Akido, and Judo for near on 20 years, yet his punches and kicks are a little bit pitiful, and totally not for lack of strength.
I am training in Muay Thai and BJJ with a little bit of background in Krav Maga and Defendo. I agree with you that striking and grappling are two different worlds, but I feel that the latter still correlates more with BAB than with Athletics. But like I said this has nothing to do with Size anymore.