I think you can just do more content with a main. Now given there are exceptions to that like pures who PvM anyways, however it's just nowhere near as efficient.
In terms of PvP, I never really liked high DPS fights like pures. You're either constantly eating, or the other guy is.. In main fights you can go for a few hits without anything happening and is just slower paced. Of course there are always exceptions to things like that but overall I feel that's how it was...
I enjoyed Pking on a main but that's strictly preference, I also liked PvM more than PvP.