Sorry but at this point my money is on the Post Office being incompetent and dishonest. They have form given the ongoing Horizon scandal.
- This is a newly introduced system
- There's no evidence it has ever worked correctly
- I'm not seeing any corroborating evidence, e.g. people being prosecuted for making or selling forged stamps
- I'm not seeing an explanation offered as to why such forgery is only happening now as opposed to before barcodes were introduced
It's not that you're wrong. It's more that I don't understand what you're proposing as an alternative. To add to the comments here pointing out that that's how CDNs work: for many designs of website, the CDN essentially is the website, being served from a cache by the provider. Even when this isn't the case, you would normally have a load balancer in front of whatever was serving your website so that if you need to swap out the server for maintenance upgrade, etc. you don't need to tell who your visitors to go to a different address. In that case, your certificate would be attached to load balancer rather than the server behind it.
If this was a 1990s and I were trying to run my own server on my own hardware in my bedroom, you might have a point, but please explain how you would implement an alternative in any meaningful way today.