Nobody is suggesting to Parler that they build anything like the equivalent of a payment processing network.

They just need a hosting service. If they relied heavily on specific services provided by AWS, they would need to either recreate them or reengineer their code to do things differently.

These are on an entirely differently level of "just make your own" from "make your own payment network".

Unless, that is, there is no hosting service that will have them (and maybe no colo facility that will allow them presence). If so, then I would view the situations as essentially equivalent.