what types are least capabale of successfully typing other people's types

[garbage]

I think I'm pretty good at reading people, but pretty bad at placing them in preset categories, definitions and applications of which are contradictory from one person and source to the next. If mbti were objective, that would be one thing, but it's not, so I'm the first to admit I have no idea how to determine what type to place most people in. I have no idea which system to use, as there's little solidity and consistency even between those who consider themselves experts.

Also, although some people are pretty strong in one or even all categories (whether dichotomy or cog function), I think many waffle in grayer zones where they don't have crystal clear preferences in one or more. At least in the sense preference/mbti is talked about and practiced on this forum. And in those cases, I question the need to even bother with placement in one set type. What purpose would that achieve in the end?

This. I don't particularly care so much about what someone's type is; I care about having appropriate vocabulary and frameworks to describe them in my head--which supplements people-intuition by allowing it to be placed into words and, to an extent, formally explained. I use a mish-mash of MBTI, Enneagram, Big Five and others when mentally 'placing' people.

According to the most objective measures we have for type, people can be described as 'strong T's' or 'weak N's'. Wake me up when we come up with a typing system with an actual bimodal distribution; then, we can answer the question of who has the best typing skills.