I have played Annihilation Marauder in SWTOR (literally requires the most buttons out of any spec in the game) without a Naga or G600 just fine. I do have one which I bought to simplify the mashing, but it is definitely possible to play without one assuming you can hit binds like Shift + Z and such pretty quickly. So, MMO mice are not necessary in my opinion, but are definitely easier on the hands. I will say that I found I could only comfortably use some of the buttons and it was really difficult at first to play with it because I wasn't used to my thumb being so active on the mouse.
As far as other gaming mice go, I own a g400 which I use because it fits my hand extremely well and it has a "perfect" sensor for competitive FPS which I also play a lot of.
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