But The Nexus never focused on any of the members of the group other than Wade Barrett before Punk came, and by that point Wade was gone. That group was doomed to fail, way before Punk took over it. Can't compare the two in any way whatsoever.
I'm sure if someone like Randy Orton took over the group that Reigns, Rollins and Ambrose would still get a lot of attention, if not more. Right now they've played second fiddle to pretty much everything even while being the most entertaining thing on the roster, with someone like Orton taking over the group they could garner a lot of momentum if Orton is pushed accordingly.