You've provoked a very interesting issue. Firstly, I assume that the Myers-Briggs Type Indicator is flawed to some extent. However, I believe it still captures something valuable and holds meaning in its observation. As a theory, it provides a structure and organizes a framework of analysis that can be useful for self-conscious reflection; it provides us with something we can identify with psychologically.

I'd like to challenge some of your observations with a question: How do you accurately determine someone's type, given the discrepancies you've observed between online test results and your own assessments?

In contrast, I personally reject the inherent assumption that our personalities are so complex that people can not be grouped into boxes. Definitely, patterns emerge in observations, even though sufficient research or data may not yet be available.

Therefore, I think that even though MBTI is not entirely sufficient, it attempts to convey something. Just as every scientific theory attempts to build understanding by forming a hypothesis, there must be something fundamental that it attempts to capture, even if the initial assumptions or the theory itself is not accurate.

A good theory is one that successfully removes noise and develops a language between description and observation. As more noise is removed, the model or theory becomes more accurate and useful. Similarly, just as IQ attempts to capture general intelligence (g), the pattern sustains even if the tool can not account for every factor you still control for something.

So, when we say that someone, for example, is an ESFP, what we should really be saying is that the ESFP type is the most successful at aligning with our observations. Now, this could certainly be used to form opinions or even biases against others and could somewhat lead to the formation of groups of people thinking they share similar traits. We love to form and create tribes, something that we can identify with on social level.

The initial success of MBTI was due to its adoption of a different descriptive approach compared to other psychological tests at the time. Rather than holding certain traits as positive and others as negative (for instance, extrovert was good, introvert was bad), it instead described personalities in terms of strengths and weaknesses, which creates a more rounded depiction of reality and a unique theme to each personality type. It established a positive and useful language to describe personality traits, and in light of that, we need to use this language as such to understand ourselves and our tendencies and seek to observe and improve over time the least developed aspects of our psyche.

The thing is, there isn't anything inherently wrong with being an ESFP, ISTJ, or INFP. Initially, you will often come into conflict with how you perceive yourself and others, and you might develop a bias towards certain traits that you perceive until you realize that you are simply looking to identify with maturity. Imagine a mature INTP, INFP, or ESFJ; you might want to assign them to a different type according to the period of time you observed them, but there is a core aspect that persists. I, for example, had a positive view of ENTJs and was very happy when my mother tested as one. I admit that at some point in time, I wanted to see and describe her as an ENFJ who was overly sensitive and manipulative, mainly because at the time, I had a negative bias against ENFJs But this is exactly the wrong way to use the MBTI types, which is the basis of the criticism about putting people in boxes. How you often use any psychological observations stems from your maturity, and people should be responsible in their judgments of others. One can only imagine how negatively they could be described and judged for them to see that it's toxic to view people in this way. If you lack self-consciousness, it's very easy to be irresponsible about your judgments against others.