Ive designed motion control systems for 25ish years. I hope it makes you feel like a read a book or two. How come i feel like you are trying to have something to say in a topic you dont understand by feeling something? A google search will provide you with lots of results around positioning and inertia matching in motion control because the guys posting DIY topics for robot people may have read about it or had someone explain it to them. It applies to all electric motor powered devices but the ratios are different for each class of product. But it always has to be followed whether someone knows its applied or not.

If you want to know then ask. Here are my feelings on your comments;
it doesnt apply to accelerating a car as quickly as possible- its importance depends on the motion profile and the exact ratio along with it. If an electric motor starts and stops and is coupled to a drive train which obviously has a mass including the mass of the motor then it is the 1st most important piece of physics. If the motor and the rest are at a constant velocity its the second most important piece of physics.

Its true you can put a 10hp electric motor on a conveyor that needs 1hp. What happens every time a coil aligns with the rotor and induces a torque? What happens to gears? What happens to belts? What happens to wheels? What happens if the motor doesnt shake into failure? So you are feeding a big pulse into a weak system. What if it can handle that pulse and magically no other problems like traction get in the way? You are winding up a rubber band that is going to feedback into the motor and collide with the opposing forces while all the while one side has a very high inertia and the other side doesnt.

I used horsepower to visualize the issue only. You can have a very heavy rotor with very little torque and vice versa.

I suspect the gear train is too heavy but I clarified that too much or too little is a problem. But you are still right. We have weight limits. You can tune your power train like you tune the rest of the car. You can make it easier to drive or you can make it wildly powerful. Its like measuring camber. Once you know what you need for a track and how it feels you can go back to it every time. Once you figure it out you can repeat it and do other things. Once you find that a 10:1 ratio feels right at your favorite track you wont be going to 1:1 to go faster at that track.

if you had a track that never had a straight and was continuous acceleration followed by deceleration something below 10:1 would save you a couple 100 ms per accel/deceleration. A track that is just a straight line could be 60:1 if it never need acc/dec. a track that is equal time at acceleration/deceleration as opposed to continuous speed 30:1. But the right inertia mismatch adds milliseconds to every single accel/deceleration.

there is no way around practice to build consistency. You can push the mechanics as you get better or you can limit the mechanical system to build confidence and consistency but either way...

​​​​​​​downhill racing puts more emphasis on inertia matching.

I know electric motor applications. its not a requirement. Go have fun. If you want to know something I’ll share but keep in mind that Im not here to make any difference to the hobby. i race for fun and practice to get better. My points are to specific questions for specific people, if someone else gets something then thats even better but I dont mind people saying things i dont understand or disagree with and I dont need everyone to get caught up in what I write. It hits some people in a good way and some people in a bad way. im not here to discourage anyone.

Anything that can be felt by the motor in the form of inertia is ratio’ed to the rotor primarily through gearing. I suspect you are correct though.

Downhill racing.... my mind is blown.

I thought the only thing you tested at the track was the durability of the pipes?