So your description of his response really struck a nerve with me. The founder is the leader of the company, not the board, and the founder(s) regularly give up equity in order for a company to be successful. Yes, it might require board approval, but passing the buck to the board like that is inappropriate.

The matter at hand is: does he believe you deserve more equity at this point in time? If yes, then commit to fighting for you (and if equity is somehow impossible, explore other options). If no, explain why & how to improve.

To be fair, nobody is perfect in every interaction, and there are a million rational reasons why a founder would sidestep a question like that (terrible board relationship, you or others at the company have a hard time hearing negative feedback, distracted that day, etc.). If you feel like the matter wasn't resolved to your satisfaction, it is worth bringing back up.