I just got back playing last 3 weeks ago done the sq's up my sbook4 to 5, tested it out, it really does scale up on Neutral Magic
check also this video I saw from a friend of mine youtu.be/e6L9wKKgceI he even compare a full 2s matk set vs 1s neutral m set, neutral m set deals far more better dmg for gc
Ok after several test it seems that yes natural magic does boost the per ailment dmg portion, but not the matk portion.
When switching to neutral magic gear GC base dmg would decrease, but each ailment added would do more dmg. So as long as you have at least two ailments on the mob natural magic dmg will do more dmg otherwise matk will win.
Don't forget when building a neutral magic set that all magic includes neutral magic. Therefore a spell king ring ns will give more neutral magic(10%) then a 1s spec with neutral enhance iii crystal(6%).
I guess I never noticed before because I already have 24% neutral magic in my matk set.