I see a tendency for people here and elsewhere to assume that these three systems are all about the same thing, and that with a little bit of effort, they can be rephrased to arrive at a "common system" that combines all of them. People are saying MBTT is "wrong" because it doesn't take into consideration some things that socionics does. Socionics descriptions are "wrong" because they stray from Jung. Etc. etc.

This is incorrect. The systems appear similar, but they are not the same. It is incorrect to say that MBTT descriptions are "not quite accurate," and that by "helping them out" with some socionics concepts, we will somehow improve their system. Or that by sticking to Jung's functional descriptions, we will "help out" socionics.

Each typology is autonomous and stands on its own. The correctness of any assertion within any of these systems can only be judged from within that system. There are three different concepts of introversion/extraversion. Three different concepts of J/P or rationality/irrationality, etc.

Even if the descriptions of these and other concepts appear to be nearly the same, there are always implicit assumptions and unstated practices within each system that differ from the others. In other words, you can have two very similar descriptions of extraversion/introversion, but very different approaches to identifying this dichotomy. Socionists have different criteria for identifying dichotomies than Meyers-Briggs typologists. Although socionists also differ among themselves, they collectively gravitate towards a set of approaches that is distinctly different from MBTT or even Jung. Each typology and set of practical approaches is internally consistent. You cannot say that a socionics approach is "wrong" based on a Jungian or MBTT understanding, -- only based on a socionics understanding.

Socionics can define its terms any way it sees fit. The only ultimate criteria for evaluating the "correctness" of socionics definitions are, "Is this logically consistent with the rest of socionics?" and "Does this help explain interaction?" "Because Jung says it differently" or "because my mother is not like this, but she is INTj for sure" are not really valid arguments.

Likewise, MBTT can define its terms how it pleases, with its somewhat different criteria -- "Is this logically consistent with the rest of MBTT?" and "Does this help explain personality?"

These are two different paths, and they lead to different places.

I'm basically reacting here to people's attempts to create their own home-grown strains of socionics (usually mixtures with other typologies) and promote them as "socionics," while ignoring accepted views among actual socionists.