With hybrids it's more than just the battery and motor-generator(s). There's a reason they feel lethargic with a drained or dead HV battery. The engine is tuned for fuel mileage (e.g. atkinson cycle) which you can't do in non-hybrids without making them feel lethargic or some other disadvantage.
In other words, taking the battery out of the equation may make only a 10% change, but it isn't the only part of the equation.
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