It’s wrong because hydrogen in the first stage optimized for things you don’t care about, namely propellant mass. In exchange, you get heavier tanks, physically

It’s wrong because hydrogen in the first stage optimized for things you don’t care about, namely propellant mass. In exchange, you get heavier tanks, physically larger engines, and (obviously) more complex operations. Yes, it has the highest practical specific impulse. No, that is not the most important metric for a lower stage. Take a look at how many new launchers are using hydrogen in their lower stages. Hint: it’s a big, round sort of a number.