I don't get why people are viewing map simplicity so negatively

I think people are mixing the topics here. This is not about CWK specifically. It's about MAP DESIGN.

The entire point here is that Crimsonwood was the absolute best example that large well designed maps were possible to make that were as good, or even better than generic flat maps.

Typhons, Elder Wraiths, Windraiders all had ridiculously shaped maps, but were all better than average training areas at the respective levels at various times, and those were just the more popular ones. Every monster in CWKs mountain area was trainable, regardless of the map size.