I don't think the issue was a technical difference of opinion regarding whether transformers alone were needed or other architectures required. It seems the split was over speed of commercialization and Sam's recent decision to launch custom GPTs and a ChatGPT Store. IMO, the board miscalculated. OpenAI won't be able to pursue their "betterment of humanity" mission without funding and they seemingly just pissed off their biggest funding source with a move that will also make other would be investors very skittish now.