I like how some of the services are very cheap (S3, Lambda), but then at some point you end up using a bunch of other complements, one of which is very expensive and makes the profit.

At which point, as you say, the cost and complexity of a move is huge so you are stuck with a recurring bill.

Another interesting thing is that you pay for 100% of a VM virtual CPU even if it is only utilised 40%, but the cloud is selling your other 60% capacity to another user.

They have no incentive to charge you “based on CPU usage” for VM’s that are always on, even though it is possible. I think this would be a better approach than Lambda - to dynamically add more cores to your OS as you need them.