The Python interface is the only one that addresses my criticisms, but do people actually use it? Is it well supported, stable and so on?

The YAML is the default, and it's what you find examples and support for (Stack Overflow and so on). I get the impression that many of the renderers are not "official", in the sense that they're maintained by other people.

If Salt only provided a Python API, the situation would be different. As such, it's a case of too much choice, and not enough standardization. There are no less than three competing Python renderers.