Go back and watch the countdown again. Randy Couture himself got his first HW title fight in only his 4th MMA bout. Randy was 3-0 and Brock was 2-1, but with fights against Mir and Herring I'd argue that Brock faced much tougher, more experienced opponents.
Who else was there to get the shot? Arlovski and Sylvia are gone. Mir and Nog were already signed to fight each other. Herring lost to Brock. Kongo lost to Herring. Velasquez IMO is just as green as Brock. Hardonk? Eddie Sanchez? Ha! The only guy who had a legit claim to this shot over Lesnar was Werdum (having beaten Vera and GG) but we all saw how great he looked in his last fight.
If you think someone else deserved that title shot more: name them. The simple fact is that Brock's quick rise has nothing to do with marketing or gimmicks; it has everything to do with how SHALLOW the HW division as a whole is right now. That's not Brock's fault. Don't hate the player; Hate the game.