Problems with Craft CMS development strategy
I do not know where your problem is? In Wordpress, you can build pages with CustomFields, and I think the same with Drupal.

Because you will have the same problem when Devs delete fields and play on the live system, the content is missing or the frontend error generated.

Therefore, it is simply forbidden to simply delete fields, they do the same nevertheless is not the CMS to blame, then that is Human Failure.

If you are familiar with the principle of the ContentBuilders (no static backend masks), then you would not get far with field configurations with YAML or JSON, then the editor determines which fields he needs for each article individually.

I'm not sure if it's so much performance gain when you put the fields into the filesystem, because Craft has to double into the filesystem for the representation of a field in the backend (general fieldstyle, the field configuration) and then into the database To pick up the content.

Craft 2 is fast, Craft 3 is even faster. Anyone who builds fixed fields does not have to worry about the backend performance.