I'm not going to claim that IQ quantitatively describes some useful aspect of individuals. I'm not trying to justify a natural aristocracy. Moreso if we actually did identify this relationship between long term success and high IQ scores then maybe we can identify paths to success through other measures.

Again more conjecture, but maybe IQ has more to do with concentration and abstract thinking. If there were a relationship between wealth and childhood trauma/stress that could impair abstract thinking, it would make a good case for policies designed to prevent childhood trauma, in particular those brought on by poverty.