please tell me they're prioritizing minimizing the existential cost of the climate catastrophe over the $ cost

I'm sure you know that's not the case. It's always about the money.

That said, I would guess that these function similarly to hybrid car engines. Electric motors are better at providing a quick or variable torque rsponse and gas engines are most efficient running at a constant RPM. Put those properties together and you get an electric motor designed for takeoff and large altitude changes, and a gas motor designed for maintaining cruising speed.

Essentially, the exact opposite of what you wanted.