Why are u comparing him to sapp/tito? I'm lost.
Is he improving? Well seeing as he lost the first fight to Mir, then beat him in the rematch and took the HW belt in the process. Yeah, I'd say he's improving. He beat two tough top 10 fighters, convincingly.
Couture never out-grappled him, go back and watch the fight. Sure, Randy could manuvere a bit, but Brock had control of that fight. He pushed him up against the fence and finished him.
Against Mir, he didn't just utilize wrist control. He used his whole body very effectively, he kept patient, picked his shots and kept his hips and body pressed against Mir, giving him no room to breath or actively look for a sub. Smart strategy, planned well.
He's improving, but it's just hard to really pick one moment where he improved. It's MMA, anything can happen, you have to be ready to adapt to it. No one could train MMA as much as he did, and not improve at all.
I probably was being sarcastic in the above post. I think you should flame me for it.