Bank transfer is fine if you want to do things, less so if you want to do “things”. If you wanted to buy a car a transfer would be fine, but if you wanted to “buy a car” then probably less so.
Whether or not we agree with the morality/ethics of this, it’s still his money and I believe Monzo should be offering an option to accommodate this. I think the reason behind the daily cash withdrawal limits are to reduce the impact of fraud, so maybe Monzo could have a feature to raise the limits after being given notice in the app?