5. "In this course specifically, you would have every tee, bunker, green, fairway, rough and even some water in a multipolygon relationship with each other. This is not feasible."

Yes, that is the end goal and is very feasible. In fact, I will show you that it is easy to accomplish using existing tools like JOSM. (Life with JOSM is so much better than the built in iD editor. I'd suggest looking into it.) I'll add a comment when I'm done.

6. "The multipolygon relationship is supposed to be used by the same type of tagged area that has obvious inner and outer boundaries. Like a lake with an island. A building with an atrium, etc."

Fairways and greens are one of those obvious inner and outer boundary use cases. (Where the fairway surrounds the green specifically. I realize that many fairways simply butt up against the green. And some fairways don't even reach the green.)

7. "The fairways that share nodes all the way around greens (even the ones mistakenly tagged as tees) are another problem."

Yes, I'm well aware of those. I review golf course edits (in the US) every day and have started leaving comments with new instances of that error and try to educate people so those won't be created any longer. My current major focus are the 20,000 fairways that are sloppily drawn across greens. After that, I will address those, but it will likely be later this year.

8. "If you want to be accurate, these nodes/splines need to be aligned with the most recent official elevation data, not whatever old sat image OSM is able to freely use. I've seen many splines be off by 20 yds or more."

Yeah, that has always been a problem. I only one man. I can't solve all mapping problems. My main focus is to get the geometries represented correctly and hopefully there are others that can work on getting everything properly aligned.
