That can be skewed when you only throw a couple of punches per fight.
In the Herring fight Lesnar threw 95 punches landing 40 of them.
In the Couture fight Lesnar threw 86 punches landing 45 of them.
Theres no data from Lesnar/Mir 1 though.
In Mir/Nog Mir threw something like 115 punches landing 65 or so (just going off memory)
To say that Brock has improved his sub defense (with no valid fights to back that up) and then to turn around and say that Mir's standup has not improved (when it is obvious that it has judging by his last fight) is, IMO, not valid.
I dont think Mir's stand up is all that good, even watching the Nog/Mir fight again. He learned to throw a combo against a BJJ guy. It was a solid game plan and worked well. I dont think Nog expected it. Wouldve been a completely different story if it were against Couture. I dont think we'd be talking about Mir's stand up at all.
But your point about Brock being a 1 punch stand up guy is false. Of those stats above, it was about 50/50 in regards to stand up/GnP.