After trying to write complex loop statements and conditionals in yaml for ansible I had this thought as well. It's nice when declarative configurations work, but once they don't and you have to try to write a real program in yaml you'll want to pull your hair out.
This was my exact experience as well. I was an early user if sensible and loved that it was yaml. Then had to deal with jinja inside yaml. And finally a syntax for loops appeared!
I have run into the same type of issues with salt.
