Not true. Electric motor efficiency is still very good at high rpms.
The Tesla Roadster HAD a 2 speed transmission. It was a huge reliability problem so they dropped it. ICE’s have transmissions because they don’t develop much torque at low rpms, electric motors do develop high torque at low rpms so there is no need for multiple gears.
And there is an efficiency loss every time a gear is involved. Notice none of the EV makers use a multiple gear transmission.
No. Top speed is limited by how much horsepower can be applied to oppose the wind resistance. A 100 hp electric motor will have a similar top speed to a 100 hp ICE if each were geared to reach max HP at the rated max speed.