Being uncommon is not the issue. The issue is that it throws a wrench into the natural meta-identification process which is based on an actual learned skill you can get better at by paying attention, studying the guides, and getting in-game experience. Autolocking armor, on the other hand, is a completely random, highly unpredictable way to mess up your game, where the only way to completely safeguard yourself is to avoid doing what is actually fun and rewarding. It's not that it's inherently bad to have such an element in a roguelike, but rather that it has no place in early game where, even if you are an experienced player, you are likely to die earlier than getting provisions for removal (or succumbing to those provisions, in case of attempting trap-based destruction), and if you are a newcomer, it's just unnecessarily frustrating and fosters the feeling of not being in control. Not to mention that it gives even more advantage to the literate and pious characters who can ID earlier and more efficiently than the others. So all in all, definitely a correct decision on TB's part.
EDIT: The exact same thing is getting destroyed by a random stone block trap on the upper levels of the dungeon that can kill way too many late-blooming builds in one hit. Things like this add nothing but frustration because you know you can't get better at this to avoid the next time.