If my 2k gearless ebike can hit 45mph how is it your 5kW scoot can bare touch 52mph?

Two major factors here (often overlooked) is total wheel size and total.magnetic.flux.

Wheel size is complicated because it is not just about a longer rolling distance per rotation, but there are also factors like much less rolling resistance, more rotational mass and momentum and even aerodynamic factors.

There's a reason why a skinny tire 700c size wheel bike will coast for hundreds or even thousands of feet and be more efficient per watt/distance and a small wheel stand up scooter slows down so fast when you try to coast it feels like you're hitting the brakes.

Even an analog push scooter without motors has so much rolling resistance that you can't really coast except down hills steep enough to overcome that drag.

Meanwhile a 700c analog bike will coast down practically any grade no matter how.small once you start rolling and you can cover miles and miles without pedaling at all as long as there's just enough slope.

As for motor and magetic flux - Watts is a very poor measurement of actual efficiency, power or total speed because electric motors widely vary - especially brushless DC motors of varying sizes, winding types and magnet sizes and strength.

The issue is that every brushless DC motor has a flux saturation limit that is the true limit to how many RPMs a motor can do (efficiently) and not melt down.

Smaller motors are going to reach this saturation state sooner larger motors, and on a watt per watt basis they're going to max out of torque and total speed sooner than larger motors.