Not even close. Having tech themed gear != being a tech themed class.
A hunter is a hunter. You get 1, maybe 2, pets. Those pets can be mechanical, but are still normal pets.
A Tinker, as many would imagine the class, would be closer to, say, the current iteration of Demo Lock, but heavily tech themed with a Mech Suit and guns.
The point is that a lot of the robot pets (more minions than pets) wouldn't have a pet bar. The idea would be similar to the Engineer class from Torchlight 2. And your argument is basically, "That class is redundant because of my transmog." Can your hunter act as a healer for the group? Can your hunter properly tank an instance? Not your pet, but your hunter?
The Tinker class would also give them the opportunity to add a new weapon type, 1h guns that can you can DW. That would be a benefit for Hunters as well. And hell, Outlaw Rogues could be tweaked to utilize pistols as well, perhaps a pistol in the offhand, sword in the main hand? Would definitely feel more "Pirate" like, which is the obvious theme there.
The opportunities for what could be added to the game with a Tinker class far outweigh what would be added with some weird hybrid of existing classes, dunked in purple. The Dark Ranger class that people have mentioned always ends up being "It's Markmanship, but this time, in Void flavor!" Additionally, there is zero logical way you could explain the Alliance having Dark Rangers, as they are literally Sylvanas' personal guard. So what? Back to different classes for each faction?