This theory is really interesting but….not enough evidence to support it…Infact her craziness was questioned… but in a few episodes before season 3…. And the season after Ross and Rachel’s baby was born, Phoebe was more funny and a little bit sensible, a little more like Chandler…. Joey on the other hand never matured the whole show and also had a lot of moments that are stupid…the argument you have for your theory can also hold for Joey… but what do I know😂