MDL-45067 started as a simple fix of the 2x2 matrix button, then turned into a TeX 'brain-dump'!
I posted the screenshots with the specific aim of encouraging some reorganisation and 'whittling-down' of the buttons. I'm a scientist, not a maths-specialist. My experimentalist nature likes to tinker with something that exists. Many of my expectations of and preconceptions about e-learning have proved wrong.
May well be difficult to come up with one layout for all educational contexts. However, given the easy configuration of the new Moodle equation editor, I'm sure we can come up with a default for Moodle 2.7 that's as good as, or better than, the existing options such as DragMath, Wiris or CodeCogs. By all means post suggestions here or as comments to MDL-45067.
Simply moving some of basic options on the 'Advanced' tab to the first (leftmost) tab - and stripping out most of the relational operators to later tabs - should make things less intimidating.
As you suggest, if it's still scary, complexities can end up in the Moodle Docs. Though, to be honest, I have found the existing docs on Algebra,TeX filters etc are already pretty scary. Maths can be a complex business .
So, I still think it is useful to have good working, exemplars of at least some advanced features in the default editor.