The client hating it just means you're smarter than them and should press on to help them outgrow their ignorance. It's a good sign.

YAML definitely felt less intimidating to me than XML, when I first saw them.
But the YAML examples also had much less information in them than the XML ones.
But not having to type all those brackets definitely helps. In case of XML, I am always looking to just get a GUI going for it instead, because typing it out feels cumbersome (I'm from C++)