I have a rule that is simple, effective but also quite rude: if you can't deliver and maintain a 500 instances large infrastructure, same uptime and all, at half the cost of AWS by yourself (1 person) in 3 months using only open source solutions basically you should not have an opinion about this. You are just rationalizing your incompetence on this particular subject. Sorry to be this blunt but I am simply tired of…
I don't consider this rude or blunt, but rather incomplete as I really am not sure what points are frustrating for you or what you would hope someone takes away from it -- I'm an outside observer on the cloud subject as I have seen huge debates over use of the public cloud internally at my company and also with client companies. I've seen the billing costs of the public cloud absolutely demolish an IT org's yearly bu…
You need to be able to do both options before having an opinion on which is appropriate in which case. I am suprised to have to state this. But in my experience people argue one option a lot without being to deliver the other.
People who know bare metal are rare these days from the total of available infrastructure engineers (call them sysadmins, devops, etc). I guess this justifies companies looking at cloud a little bit. But if you really search you can find engineers sub 100k per year being able to deliver 100k per month savings compared to AWS.
There are also engineers who stayed away from cloud and can't deliver that option. A lot more rare though. The same level of wrong if they argue against cloud from ignorance.
The right choice for serious infrastructures is always both these days. Have the bulk on premise for steady loads and 95% of features, expand to public clouds for dynamic scaling and features you don't want do do yourself, at least yet. This combination offers good costs, flexibility, covers possible future needs, etc