As you mentioned, the term tank pre-dates WoW, but so does level limits on magic items (EQ is a great example where most items had level limits).
Level limits on magic items is pretty much 100% "MMORPG Influence" because it's almost always done to prevent 'twinking' - that is, giving inappropriate high-level gear to low-level characters to make them exceptionally powerful and make the game exceptionally easy for them. (Stat-based limits are a combination of both: you need sufficient stats, which is like a level cap, but you also need *those* stats, which add character building decisions.)
And I mean, certainly World of Warcraft isn't the first MMORPG to implement level limits on magic items - heck, I was playing on an MMORPG with level-limited magic items in
1998, before even EverQuest came out - but almost none of the people who're going to be whining about "MMORPG Influence" are honestly going to be happier about
EverQuest influence on their games than
World of Warcraft influence. So, honestly, I don't understand why anyone would even raise that as a defense.
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If I had to complain about something's influence on D&D, I'd whine about what I perceive to be the influence of M:tG's design team and its throwaway name choices on recent D&D's monster manuals. I guess I just don't love compound words as much as they do, don't care for "hit the thesaurus" names, and (Race name) (Pseudo-class name) do nothing for me - heck, in many cases, the last annoys me even more because it creates pseudo-classes with neat abilities PCs can never have, even when it'd make sense, since they're only present as an ability of that one monster. So MMV can keep its Frostwind Viragos and Scouring Stanchions, Desert of Desolation can keep its Yuan-ti Malisons, and 4e D&D can keep its Cambion Hellswords. Those are all terminally lame to me in ways not even the stupid stuff in the original Palace of the Silver Princess can match.