Daodao appears do be a high damage weapon with machete like design. So, why is a thinner and longer bladed miadao do more damage? Doesn't make sense.
Could you flip it so daodao does the high damage and speed. This will balance because its shorter than the miadao. Of course, adjust prices accordingly.
It's a combo of realism, balance, and variety for the stabless curved 2h. Otherwise the obvious choice is miadao.