CM Punk can handle the mic work of a leader. He has the followers like a leader has. He stands out like a leader.
But CM Punk is a shitty leader. By any way you want to judge it.
Has Punk won a belt in either of his groups? No. How do you have 2 seperate factions and stay out of the title scene more than Punk. At least when Barrett was running the Nexus, he was getting title shots. Punk hasn't had a one on one shot at the title while in S.E.S. or the New Nexus.
Has any member of Punk's groups looked strong by defending him? No. Gallows: Released, Mercury: Released, Serena: Released, Gabriel and Slater: shipped over to Smackdown to win the tag titles for another group, Husky Harris: Sent back to the minor leagues, and so far, the current Nexus is getting lost in the background of this Orton/Punk feud. At least under Barrett's leadership, the Nexus/Corre has won the tag titles. Even when Orton had Legacy, he was vaulting Rhodes and Dibiase into the upper midcard feuding with DX and winning the tag belts.
Punk's groups have never held a title. Remember when groups would become so powerful, they would own them all? DX would have HHH as the world champion, the new age outlaws as tag champs, X-Pac as IC champ, Steph as women's champ, that alone drew so much heat, nowadays, we lose interest if you aren'e competing for something interesting.
The Nexus was huge when they started because they came onto the playground, picked the biggest bully and beat him down. Who the hell wants to see that same group, change leaders, lose their entire purpose and then just be drones to fight that man's battles that have nothing to do with that group.
WWE really drops the ball with Punk. S.E.S. could have been good, but after you win nothing for 8 months and your followers aren't have less in ring talent than Mickey Rourke, we don't care anymore. Now with the Nexus thing, You only have one original member left from this group that had a higher purpose for destroying the roster. Now their higher purpose is looking like shit while Orton plays the Batman to Cena's Superman, ridding the WWE of the evil garbage infecting it.