He kind of touches on this in point IV, but never mentioned specifically: the cost comparison is not AWS vs ovh. It's fragment-of-EC2 vs ovh. If you need a predefined small number of VMs and no other functionality, it would be silly to go with AWS. But on the other hand, if you want a set of servers of a given class spawning on demand, with traffic coming in via load balancers, with integrated certificate and DNS man…
That and the 9's. I don't know how good OVH is with outage and availability. Sure the raw compute is cheaper.
There's also storage. He's renting physical drives on OVH meaning he has to take care of replication and back-up himself. The disks in his AWS VMs should be persistent. If his OVH server goes down due to hardware failure, what happens to his disks? I genuinely don't know.
Lastly, OVH doesn't have regions everywhere. Then it's yet another different provider with slightly different product for every geographical region he wants to support.