If you listen to Musk in this recent 21-Nov-2021 talk and Q&A etc with (US) National Academies of Sciences (etc)
(or
https://forum.nasaspaceflight.com/in...?topic=55237.0) he discusses the issues with composite tanks. It is a long talk and worth listening to in its entirety. In respect of the tanks he notes the porosity/leaks aspects, the flammability aspects (LOX + carbon + high pressure = bang), the weight, the strength (at pressure + low temp), the cost, and the re-entry (heated strength) and the overall airframe weight fraction that comes from this. That is what led to Space-X's decision to ultimately select and develop a stainless steel grade for the Starship as he explains. He also explains the corresponding decisions on Falcon 9. Remember that Space X started off with some very big composite structures in the early stages of Starship, back when they were going with conventional wisdom, so it is not as if Space-X didn't try the composite route. You can see some of the composite tooling etc that was their original pathway for Starship in (
https://www.teslarati.com/spacex-all...p-super-heavy/ )
So you could say that the lessons of X-33 were learnt, eventually.