hardware wallets have spotty support for presentation of EIP-712 requests
I don’t see how not using EIP-712 improves the situation for hardware wallets. Wouldn’t it make more sense to specify 1 specific EIP-712 struct that is expected? In this case hardware could optimize for this one. The issue for hardware wallets with EIP-712 is that it is fully dynamic and therefore quite complex to implement with limited resources. But if you pick one specific domain+struct it is trivial to implement. This would also allow easy support on contracts (as EIP-712 was designed with smart contract in mind).