He's not paying "$100/month" for dynos. If he wants to avoid spin downs, he has to pay for a dyno. That's not hidden.
" But I believe the policy of spin downs should depend more on if and how much you are paying, rather than if you are paying for a specific element of their service, in this case a dyno."
You're seriously arguing that if you buy several items from a company, they're then obligated to give you a completely different item for free?
It is easy to play devil's advocate on something like this. Technically yes, you are right, it is not hidden. What I am saying is that I find it bad form that they spin your stuff down when you are paying so much for a SERVICE.
The purpose of the dyno is not to prevent spin downs, it is a provision for background processes, think processing orders, updating information from external APIs every hour, etc.
Your comparison is obviously bogus as we are dealing with a service, not products. It is more like paying for a spotify premium account and still having to listen to ads. He is being treated like a free user, while he is paying for premium service.
" But I believe the policy of spin downs should depend more on if and how much you are paying, rather than if you are paying for a specific element of their service, in this case a dyno."
You're seriously arguing that if you buy several items from a company, they're then obligated to give you a completely different item for free?