Those who agree that Socionics and MBTI are the same are showing great Ti at work. The ideal that they're both the same, but both approaching from different angles, or incomplete. Trying to mix them together, in search for the perfect system. In my opinion, when I actually understand the foundation of both theories, read their purposes, read their descriptions, I see two different systems with some great similarities, and some differences too, and I don't see them as compatible with one another, because of their contradicting methods. However I do see same types in individuals quite often, which isn't to say they're the same theory. If anything, people will type themselves their MBTI type in Socionics, and then try to rationalize around the actual writings of the theory as to why they're that type, when they aren't. This happens a lot more than mistyping in MBTI. This does not change the fact that the types are close to one another, but not exact. Descriptions in differing systems talk about different streams of thought, and it is your choice to connect them and get rid of ideas that don't work for both of them together. So in my opinion, you're getting rid of good information that belongs there and with the current intra-theory association.
Both theories come close to one another, bring their own great insight that I respect, but can't connect exactly.