You can have a force and counter force without any change of momentum. That would be static equilibrium but it is not propulsion. There is no such thing as a propulsive force that does not involve a change of momentum.
The conservation laws are the most fundamental principle in mechanics and there is no example of them ever having been broken. Your own pet hypotheses are not consistent with them and are therefore incorrect.
Let’s go back to the situation of the two cars.
Phase 1
They are tied together by a rope, standing back to back with their engines running, gears engaged and clutch pedal released. Their wheels are exerting a rearward force on the road, which in turn is exerting a forward force on the cars. These forward forces are balanced by equal and opposite forces exerted by the tension in the rope. Both cars and the road are stationary, so the total momentum of the system (2 cars plus road) is zero.
Phase 2
We now cut the rope and the cars accelerate away in opposite directions. The rearward forces exerted on the road by the two cars are equal and opposite so the road is not being accelerated and is not moving, so its momentum is zero. Although the velocity of the two cars is increasing, they are moving in opposite directions at the same speed, so their total momentum is zero. So the total momentum of the system is still zero. The cars are both accelerating so they must be experiencing propulsive forces, but the total momentum is not changing.
Phase 3
After a few seconds the increasing aerodynamic drag and rolling resistance acting on each car will equal the propulsive force being exerted by the road, so their speed will become constant. As before, the road is not moving or accelerating and not moving so its total momentum is still zero. The two cars are not accelerating, but are moving in opposite directions at a common speed, so their total momentum zero. But the fact that the cars are maintaining their speed while pushing against drag and rolling resistance means that they must be experiencing propulsive forces.
The total momentum of the system has remained constant throughout the entire sequence, so the law of conservation of momentum has not been violated.
The only objects which experience accelerations are the cars (during the second phase), But nothing at all is accelerating during the third phase. But in the second and third phases both cars are experiencing propulsive forces.
It is entirely possible that I have overlooked something in this analysis, and if you can find it and point it out to me I would be grateful
The fundamental argument in this thread is whether the thrust for an aircraft is produced by the rearward force we exert on the air passing through our propulsion systems, or by the rearward acceleration of that air.
If we were asked how our propulsion systems create thrust we could say:
1. By exerting a rearward force on the air passing through them, thereby causing this air to exert a forward acting force in accordance with Newton’s Third law.
Or:
2. We accelerate air rearwards, thereby causing this air to exert a forward acting force in accordance with Newton’s Third law.
Both answers sound reasonable, so we need to ask a second question to decide which is the more valid.
One such second question might be “How do we accelerate the air rearwards?” The answer to this question is “By exerting a rearward force upon it”, which is of course our first answer. We can say that we accelerate the air rearwards by exerting a rearward force on it, but we cannot say that we exert a rearward force on the air by accelerating it rearwards.
The rearward acceleration of air in aircraft propulsion systems is an inevitable, but wasteful consequence of the process by which we generate thrust. Over the years increasingly high by-pass ratios and ever larger fans have been introduced in jet engines in order to reduce the acceleration of the air passing through them. If the rearward acceleration were the hero in all of this we would not by trying to reduce it.
Your own pet hypotheses are not consistent with them and are therefore incorrect.
I do not have any pet hypotheses and I really don’t think that the use of such pejorative terms adds anything useful to the debate.