As you yourself mentioned, you're carrying around a heavy cast metal thing for 100% power output when you in fact only use 70% of the power for 99% of your flight. So you lug around all that dead weight just to be able to provide you with enough power for takeoff that you don't use after that.
That assumes that the efficiency at 100% max rated power is any better. It won't be.
There's a fatal flaw in your calculus: only 20-30% of the energy in fuel turns into shaft horsepowers, whereas electric motors have 90% efficiency.
This changes a lot once one takes into account the theoretical maximum 40% efficiency of the steam cycle used to generate electricity (except a gas turbine driving a generator directly).
I don't think a hybrid plane makes any sense because the whole case for it in cars hangs on a) a car using little power most of the time and b) energy recovery from braking. Neither of these apply to planes.