I think you are reading quite a bit more into what I am saying than what I actually intended.
The question of wether or not Cloud hosting is cheaper than on-premise hosting is dependant on a whole range of factors and indeed, “doing the math” as you put it, is quite important.
I’ve looked into this question for some very large organizations, including investigating the prospect of moving the majority of my country’s Government IT infrastructure to the Cloud. Things get complicated fast. Trust me.
To zoom back in to my point in this particular post, if you would rather not deal with servers (did I mention I don’t like dealing with servers?) and you are looking at options for outsourcing — generally — FaaS (functions as a service) is a cheaper option than IaaS (Infrastructure as a Service). Because with FaaS you are only being billed for the time during which your function is running.