Yes, I mentioned some canon variation there. And yes Hondo's has a much wider viewscreen, I make those and wear one myself in fact but, it's still abstractly a T.
I've seen your helmets. You do a great job on those, by the way. Professional quality.
And as I said, I won't argue that the triangular shape of Hondo's helmet is a stylistic evolution of the standard T-shape. But aside from whatever those cylindrical pieces are on the art piece's helmet, I don't see all that much difference between that one and the design Revan wore. The "teeth" are simply a stylistic addition, possibly as a reflection of whatever species the Mandalorian comes from.
While out of universe it makes sense to have a dress code because your building from the original Mandalorian Boba Fett, having something people recognize is important so having a dress code would be equally important. In-universe it makes less sense. Mandalorians are not interested in dress codes and whether or not your helmet has a' T', but for people willing to live the Mandalorian way. The T is a tradition not a necessity.
Well, you're correct...to a point. As stated a few times throughout the Republic Commando books, and once or twice in the Legacy of the Force books as well, if I'm not mistaken, a secondary purpose of Mandalorian armor is its unique, identifying design. While there are variations, the general design has become something of a unifying symbol that enables beings from several hundred or even thousand different species to all have some semblance of being the same. An outward manifestation of being Mandalorian, if you will.