This is only a problem if you haven't taken other measures to lighten the car to compensate.

Edit: That also depends on the weight of each component. If the gas engine is not expected to run all the time, it can be smaller/lighter than an engine in a comparable car. If it is just a generator, which it seems to be, then a whole lot of complexity is saved, beginning with the transmission. Electric engines are very small for their power, which also helps.