Actually there's numerous mentions of a Tinker class on the official forums as well.
Let's also not forget the inclusion of a mechanical/technology class in several recent MMOs and RPG games.
The classes you mention overlap terribly with existing classes. Heck, every class you mentioned above already have abilities in existing classes.
Tinkers on the other hand come from an untapped archetype that has the potential to cause no class overlap at all, and properly represent a very underrepresented aspect of the game on the class side of things.
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It doesn't really work in that fashion. Its broken down by pure DPS, 2 role Hybrids, and Full Hybrids. This explains why Monks were brought in as a full hybrid (despite being fully capable of being a pure dps melee class), because there was only 2 full hybrids in the game at the time.
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Or they could go with an archetype that actually makes sense from a class perspective, and exists in the Warcraft universe.
The Tinker class.