Actually a technology-based class would be very marketable. Especially considering that there isn't one in WoW currently, and it contains multiple concepts that players want (a new physical ranged class, mail armor, new healing spec, a class that doesn't take from other classes, etc.).
I have no idea what you're talking about here.
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https://wow.gamepedia.com/Mechanical
vs
https://wow.gamepedia.com/Demon
So yeah, not just a skin. In addition, given the fact that they are mechanical thematically opens up different gameplay options.
Again, none of that applies to a turret system. You summon one type of turret versus over 20 different totems. You don't need to "feed" your turret to keep it from abandoning you. These "flaws" your mentioning are simply not applicable.
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Yep. Unfortunately some people are ignoring the facts and simply looking to hate for whatever reason.