At least on the Prius, it has power modes, one of which (and the default) severely drops the power and throttle response, to save energy. If the Yaris was in eco mode, or something equivalent, that might explain it.

Your latter point certainly is a negative and having to replace the battery but less stress on the engine throughout the lifetime of the vehicle.

If you can get by with just purely electric, it would also save maintenance, since you'd be barely running the engine at all (or not at all), and wouldn't need to regularly flush the fluids like you would with a car that's been sitting a while.