Relationships are a two way street, and dynamics like this are pretty common. It’s sometimes called over/under functioning or codependency in substance abuse. It could be the over functioner just tore the other person down, or the under functioner was susceptible already or drew it out of the over functioner. I agree it’s really difficult to know based on limited data, and all we can say is this is strange and comes across as infantilizing but if it works for them then whatever tbh. Not my relationship to care about