Compared to what? To have an underrated ground game, first you'd have to have people saying his ground game isn't good. Nobody even knows what his ground game is like or isn't like, given that he hasn't been on the ground with any top level competition. Is his ground game better than Hunt? Than Couture? Than Mir? Than big Nog? Mir steamrolled Nog on the ground, are you saying his ground game is on Nog/Mir level? Cause Brock s-s-s-s-s-SMASHED Mir on the ground from start to finish.
You say his ground game is underrated, why? Compared to what? Who are we comparing his ground game to? Who has he fought on a high level on the ground? Until we actually see what he can do, there's no overrating or underrating it. It's a bit of a mystery. What we do know, however, is that Brock can SMASH elite level grapplers.