But it's not the same mechanics, and it's not just about the fuel source.I know they're different, but gas powered engines have proved to be more efficient with a transmission vs direct power to the wheels. Applying the same mechanics, the tesla battery is just a different power source.
The huge, drastic difference is in the motor types. A combustion engine has a very peaky power curve, with a narrow band of where it operates efficiently. It really needs a lot of those gears to keep moving the RPMs into that sweet spot for a combustion engine. Electric motors are very very flat for that through most of their RPM range, so moving gear ratios does do very much through a rational range of speeds that people would use.
But at very high speeds and high RPMs, they do have some power drop off, from effects like electric field saturation, where they can't get the magnetization of the parts of the motor to have time to drop off before they get activated again. So you can do up to levels like 90 or 100 mph without much need for a transmission. But to try to make very high speed cars to get close to 200 mph, a transmission does start to become helpful to achieve that. So it's more about enabling speed than helping efficiency.