I don't believe he is running the heavyweight division. I believe if you put JDS, Carwin, or Cain in his shoes they would be in the exact same spot as Brock. Brock has 3 wins over Mir, Couture, and Herring. I think it's irrational to consider that "running the division".
JDS, Carwin and Cain are not really much more tested by top competition than Lesnar. They just all have a bunch of lower tier opponents on their lists to round it out. That shows consistency and athleticism, but doesn't tell us much more about their peak ability. I mean there is a case to be made based on experience, but I think Brock would do fine against any of these guys.
Everybody good, plenty of slaves for my robot colony?