Using that logic there would be no single engine airplanes
Your claimed "using of logic" appears to have nothing of substance beyond being the simplest of analogies.
The "sudden loss of braking" aspect aside, what does acting as a plant for self suspension have to do with airplanes?
Nothing at all. Chain brake aside, the single most dangerous thing about coasters is pedal crank positioning.
One needs to have the cranks at ~180° to brake that wheel. Braking in turns becomes much riskier.
There may be added latency in the act of braking, and there may be unintentional braking.
If one should have to get off the seat to act as suspension (because heavy-sitting warps wheels and can get frames broke),
then doing so with the cranks in position for braking can cause the rider to brake unintentionally upon hitting a large bump.
Motorizing a bicycle will ofc get it moving at higher average speed, so using the arms and legs as suspension is almost a must.
Bicycle frames can get broke hitting big bumps at 25+MPH with little suspension at all. I've done it several times, myself.
Anyway just my views on coaster brakes and why I think they are a bad idea on anything that travels faster than ~20MPH.
I know there are many exp. riders here who have been on them for a loong time and think they do a fine job. I agree to a point.
I put over 1K miles on a chinagirl with only a coaster and never had an issue. But that bike cruised only 15-20 most the time.
a front disc brake is essential
In your opinion, of course. You see, I've traveled over 200K on bicycles and 20K on MaB without ever using a disc brake.
Most those miles on bikes with cantilever or linear-pull (v) brakes. Properly adjusted, a v-brake is a lot of brake per $.
I do agree that a disc brake is the best brake, tho. We should all be so lucky to have them