The Jungian functions and the Socionics Information Elements have the same name and we are supposed to take it as a given that they represent exactly the same concepts. This is difficult to assess: I think we can only conclude that through a rationalisation process where you see various Jungian functions on spectrums (e.g. extroverted sensing as an opposite to introverted intuition) and where you understand Jung's explanation in terms of common psychological descriptions and philosophical terms (e.g. "causal determinism" that they are the same, or at least, any direct correlation to the vagaries or outright impracticalness of Jung's descriptions (especially with introverted intuition) is not really important.

As for MBTI, there are several ways of confusion that make saying "MBTI = Socionics" to be invalid. I think at best, it should be considered a rough pointer if you believe you know your type in one system. Some MBTI descriptions are written on a functional basis and are inherently inaccurate due to misunderstanding Jung's typology. If you agree with a type profile of a INTJ and are thus primarily first, and second, then clearly, you should not be a LII in Socionics. If the description has your tertiary () and inferior () functions, or even your shadow functions, the picture is possibly confused even further.

If the description is of a general nature rather than a function-by-function one, it is possible that MBTI INTJs may have a fair resemblance to a Socionics LII, although this tends to be a chunking along the lines of "Introversion" and "Thinking" and "Intuition" for example, along with statements stating that INTJs can operate in the outside world...but they prefer not to (some descriptions are more solid than this).

Tests are similarly an issue...tests scoring I vs. E, N vs. S traits etc. to give results with the MBTIs mangled understanding of Jung's typology are especially unhelpful. (Tests with such a method of scoring do exist in the Socionics world). I suppose the issue with MBTI tests is merely an extension of the issue with MBTI however.

The MBTI is famously typified by a huge emphasis on what people do, especially in regards professions, at least in the worst extremes in the very vocal corporate wing of the MBTI. It would be easy to say that despite all these differences that "MBTI = Socionics", but that would be to take all these negative aspects of the MBTI as of only minor significance. If the MBTI is unwilling to correct its fundamental misunderstanding of Jung and if the "official" purveyors of MBTI are unwilling to use their clout, then how can it be a true maxim?