> But if you start taking into account all the logistic, additional skills, people and processes needed to maintain a rack in a DC,
You've mostly described what one pays a datacenter provider, plus hiring someone who has experience working with one (and other own-hardware vendors, such as ISPs and VARs), which doesn't cost any more (and maybe less) than hiring someone with equivalent cloud vendor expertise.
> plus the additional equipment (network gears, KVMs, etc).
Although these are non-zero, they're a few hundred dollars (if that) per server, at scale, negligible compared to $20k.
> The cost win is far less evident
It still is, since the extra costs usually brought up are rarely quantified, and, when they are, turn out to be minor (nowhere near even doubling the cost of hardware plus electricity). AWS could multiply it by 10 (as in the very rough pricing example you provided).
> generally adds delays when product requirements changes.
This is cloud's biggest advantage, but it's not directly related to cost. This advantage can easily be mitigated by merely having spare hardware sitting idle, which is, essentially part of what one is paying for at a cloud provider.