I'll invite you to look at how Tinkers are depicted in game and ask you to get back to me.
IMO...the Tinker class is unsuited for a player class. Tech, in this game, has been a source of levity. Of whimsy. As a result, the Tinker class - as shown - is (IMO) not suited for a player class. It isn't serious enough. It doesn't have the respect of the players.
That's a pity. But carrying around a huge pair of robot arms on my back is not the class I, for one, would want to play. It is too ridiculous looking.
Instead, a serious take of a tech based class would be a complete from the ground reworking of the class concept. It would take **NOTHING** from the hero class save, perhaps, the name. And, given that the name is already in use with the profession, even that is relatively meaningless.
In short - I wouldn't mind a tech based class. But a WC3 style Tinker has no interest for me. It looks ridiculous, its played too much for laughs, and it comes with unwelcome baggage as a result.
For me...a tech based class would require a careful reworking.
http://wowpedia.org/Gunman would be a good take on a tech class. As would
http://www.diablowiki.net/Demon_Hunter. A steam warrior using an exoskelton (not mecha) could also work. And for healing? A simple medic. Not an alchemist. A medic. For a tech based class, I can see a pet based healer beign very posible.
But all that is just me.
EJL