Yes, as someone who helps with some software with a YAML config, the whitespace issue has caused much time in IRC spent trading pastebins fixing these.

I agree overall YAML looks pretty nice, and consistent whitespace is a strong preference (I have pre-commit hooks), breaking user (if you have them) config if they don't know about this is an issue tho.

Do note that in addition to block collections, YAML also supports the flow collections of JSON, which are not whitespace sensitive. In fact, YAML 1.2 is a superset of JSON, and you can parse JSON with # comments as entirely valid YAML.