Re: I still have a negative opinion of cloud services
I generally agree with what you're saying, although I don't think the analog to banking is quite on point. In banking, what you're storing (money) and the value of the thing (money) are the same, and the services are essentially fungible, and the additional transaction costs of splitting your money are fairly low, so it inherently makes sense to diversify risk by spreading around the money.
However, with cloud computing, what you're using is hardware, but the value of the thing is your entire application running. Also, services are not really (or just barely) fungible, and the transactional costs of splitting your application(s) across cloud providers is very high right now. Also, you will have a more fragile and slower architecture if you're spreading your application across the public internet.
I think a better strategy is that you want to make sure you can always move your workloads to another cloud, but that you may actually choose to simply run in one cloud for now. So you want an abstraction layer to issue your various automation/orchestration commands to, and you want full configuration management so you can relaunch servers easily, but that is the vast majority of what you'll really need to do to mitigate your risks.