I am convinced that people who describe 4e as MMO-like have never played an MMO. Get out of here.
I could be wrong but having been there when the lore was written, the connection between MMOs and 4E wasn't combat. It was class composition.
Each class now had a specified role: defender, controller, support, or striker. And I remember WotC specifically stating that they had looked at MMOs for this dynamic. This would wind up becoming an issue as the game continued and a lot of the differences between classes of the same archetype could feel superficial. The at-will powers available being rather similar(at least in my memory).
So I think the 4E is like an MMO thing comes from you are expected to play your class a certain way. A rogue is a striker, a cleric is a support. While in 3E or Pathfinder you had a lot more variety to "build the class wrong". Make a charlatan social rogue who isn't that good at combat beyond providing flanking. Build a tempest cleric that is throwing out thunder bolts and is more akin to a wizard in full plate than a healer. There were some paths available inside a class to try and express your individuality, but you weren't able to deviate from the prescripted role of your class.