AMF is an ISO standard, which means the full specification can only be bought from the ISO store itself.

I'm not sure about the ambiguity mentioned in the blogpost, as ISO standards are usually rather thorough. I suppose it's because most of software implementing AMF did so without the full specification at hand and assumed some things.

For me STL/AMF and 3MF are complimentary. When I design a piece in FreeCAD and want to export it, AMF or STL is good enough as FreeCAD doesn't know anything about the printer I'll be using or the settings I want. But once in PrusaSlicer it makes sense to use 3MF to keep everything tight, for example if I need to move an already configured file from home to the office.