Tinker is not defined at all because it doesn't exist as a profession or class. There are no mechanics behind it, so it remains undefined. It would be like if I asked you to define what a 'Monk' is before we actually got the class. Would we be talking about Scarlet Monastery Monks? Auchenai Crypt Monks? Shaolin Monks? The context is different in each, and none would relate to the class we actually have. There was no lore telling us that the Brewmaster Hero would have anything to do with being a Monk.
Now that we have the class, we can easily define a Windwalker, Mistweaver and Brewmaster equally as different aspects of an overall Monk class. Mistweavers don't drink alcholic beverages or fight with martial arts, but they're classed under the same umbrella as their Brewmaster brethren all the same. This is what their lore encompasses.
Tinkers have no definition as a class. You can't argue against them any more than you could argue for them. They don't exist yet. That is why I am saying it's arbitrary to define them by any current standards.
We know what Engineers are, we know what Engineers can do. There is no information for a Tinker class, so how can you say Engineers do it all when there's nothing to compare? Arguing Tinker lore before it's made would be like arguing for-or-against the Monk before their lore was made. You'd be making false assumptions based on the only relevant information available - Scarlet Monastery and Auchenai Crypt monks.
Everyone and Anyone can use Magic (Enchanting) but this does not make them Mages (Magic User Specializing Frost, Fire and Arcane). Anyone can use Technology (Engineering) but this does not make them "Tinkers" (Technologists Specializing in Demolitions, Tech-based Combat Weaponry, etc). Thematic and mechanic overlap does not conflict with lore whatsoever.Demolishing a building and building the explosives are two completely separate crafts. Everyone can 'demolish buildings'. Everyone. Anyone.