Baldor motor catalog, for 3 phase motors, a 20HP motor weighs 416 Lbs; and a 100HP motor weighs 1,573 Lbs. Don't compare this to the power / weight ratio of my motor directly. Mine has an aluminum case, is made for automotive (intermittent) duty and is MUCH more expensive. All these trade off on weight. I pulled up a representative example in a catalog to show a simple comparison.
A motor connected directly to a wheel has no gear reduction, so the Torque requirement for the motor is MUCH higher. To get more torque, at low RPMs especially, requires more windings = more copper = more cost and more weight.
When the drive is transmitted through the transmission and the rear end, you get about 14 times greater torque at the wheel because of the gear reduction. 1st gear is 3.475:1 and the rear end is 4.1:1 in the RX-7. You get the complete ratio by multiplying them - 3.475 x 4.1 = 14.2475:1 So the RPM at the wheel is divided by that, and the torque is multiplied by that. The power stays the same since it's the product of torque and speed.
It's torque that gives us the peppy starts we all like. and that's why we have transmissions is a car. Ever try to start out in a car in 4th gear? It doesn't work very well because there's not enough torque at the wheel to accelerate the mass of the car. If you had a 1,000 HP Caterpillar engine, it would pull out in 4th gear (Lots of torque), but for your 150 HP Honda engine you need a gear reduction to accelerate.
I don't know about those 'on the wheel motors'. Maybe they have a planetary gear reduction built into them. But that's my point: 4 motors, 4 gear reducers, 4 times the complexity, 1/4 the reliability. A car with 1 larger motor, 1 transmission, and 1 drive isn't necessarily worse than one with 4 of each. I think it's better.