I mean, I'm talking grown-ass women damn near 40 INFJs are like this in my experience
I believe it because I've met plenty of people in their 30s and 40s who have under-developed functions, or are otherwise "unhealthy" and act immature. When I wrote this post, for example, I was coming out of a terrible time in my life and I was shadowy but I guess the difference was I wanted to address that and heal. (I was also careful about meeting new people while in that state and would not have, hypothetically, started a romantic relationship.) In one's 40s a person should be well on their way to developing the inferior and be well-rounded in general, but people often fall apart in their 40s. (My circumstance was more specific and not midlife crisis related.) Personally, I found my 30s grounding and peaceful. I easily shed the chaos of my earlier years when I was behaving as you described. I've watched a lot of friends go through the same grounding and peaceful experience in their 30s where they focused on learning, the mind, new skills, etc, and had balanced and harmonious relationships. Honestly, it rocked. I'm sad for people who miss out on that and continue being as they were in their 20s, especially in relationships where it affects others.
That said, all humans fuck up sometimes and we all have weaknesses in character.
All this said, I find it curious that INFJs, as well as some other types, would not want to work on self.
And of course I will sound like a broken record, but I still think some of your INFJs were mistyped, so there is that. I know you believe otherwise, but INFJ is one of the most mistyped in MBTI.