Just wondering what you base that on. GSP's top control is phenomenal, and Hendricks hasn't really showed us how good his bottom game is. If Condit couldn't get off his back, I don't think Hendricks will.
Even with the same skillset a stronger shorter guy is going to get up much easier than a taller weaker guy. Comparing Condit and Hendricks is ridiculous, a tall lanky unorthodox striker compared to a short stocky wrestler. Sure GSP probably would keep him down, but Hendricks would have an advantage over everyone else in that it will be much harder to control someone with shorter stronger limbs. Even Serra was able to get off his back, he just didn't have the wrestling to be able to handle the scrambles and lost position every time.