I'd argue that often the CDN or transit isn't drop-in replaceable. So it's usually more than 2x the cost as one has to maintain two architectures (or at least a

I'd argue that often the CDN or transit isn't drop-in replaceable. So it's usually more than 2x the cost as one has to maintain two architectures (or at least abstractions). That includes the expertise and not optimizing for strengths of either, or building really robust abstractions/adapters.