I agree with all your points above. the analogy was intended only to challenge the point made that 'If Aikido were beneficial to everyone then everyone would do it and no one would ever quit.'
You are arguing that Aikido is not beneficial to everyone, and I am not challenging that. I am simply pointing out the flaw in your logic. To reiterate my point more succinctly, If Aikido was beneficial to everyone, it does not follow that everyone would do it.
If the benefits were large enough and everyone saw more benefit in doing Aikido as opposed to something else, they would. Assuming they had the freedom to do so. But I'm just being stubborn here, although I'm right. Interestingly, you are too.