I see the logic in it. For simple Key-value configurations, TOML is superior and more straightforward to YAML. You can add sub-level values and it isn't too bad (if there aren't too many), but beyond two levels, TOML becomes difficult to use.

If you really work in YAML in any sort of more advanced capacity (kubernetes, Ansible, CI/CD Pipelines) then you really need the complexity that YAML provides. You also get used to the "gotchas" mentioned here. Navigating them is fairly straightfoward.

I think the article was vastly overblown. Is YAML perfect? Certainly not. But you find a better way to display such complex data structures in a more human-readable and human-writable way. The complexity is YAML's strength, but it comes with caveats as all complexity generally does. I really think its the best we have.