This is understandable, but this isn't about speed. Many YAML files may result in high provisioning speed or low provisioning speed, after all they only give instructions to the program doing the provisioning.
You could legitimately complain about choice of YAML as a platform for infrastructure configuration so several reasons, like:
1. Not having a built-in ability to describe templates. Lots of infrastructure wants to have some sort of polymorphic configuration, and when the infra developers chose YAML to configure it, they didn't account for that. So, instead they use various template engines that strap on this polymorphism on YAML. This was also indirectly mentioned by OP.
2. Poorly structured, especially when it comes to large configuration size. It's easy to accidentally write something you didn't intend. It's hard to search.
3. Being JSON in disguise, it inherits a lot of problems from JSON. Marshaling richer type / structure of data in and out of the program is severely impacted by the primitive and inflexible type system of the format.
But, again, this isn't speed. This is just a different set of problems.
> If I were a CTO or an IT manager I'd be very worried about stuff like this.
Practice shows this is mostly irrelevant. It's hard to reach the point where provisioning speed starts to hurt so much it impacts business decisions. For instance, provisioning in MS Azure is on average twice as slow as it is in AWS. (And deprovisioning is probably four times as slow.) And nobody cares. So many other concerns will overshadow this particular aspect, that you'd feel uncomfortable to even bring it up, if you had to choose between two service providers. Primary driver is cost of running the infrastructure for a long time, overall as a system. Starting time does contribute to the total, but unless your business requires very frequent allocation and deallocation of resources, this won't make a difference. Also, cloud vendors don't bill you for the time that the infrastructure is being brought up, so, it's really hard to make a compelling case to choose the fast-to-provision infra over the slow one just based on that aspect alone.
