1. Joyboy
2. Topman. His CoC roar gave an AoE impact rivaling the one from Newgate-Roger's clash.
3. Roger/Newgate.
4. Shanks. I originally had him at 2 with Topman, but i think the AoE impact of CoC gives better indicator of which CoC Haki is more powerful, though Shanks would be #2 in mastery feats.
On an actual battlefied? Higher than Riboku's.
Unless understanding of warfare is purely about strategical, then less than Riboku's. But it's about utilizing martial prowess + your strategical prowess in conquering warfare, then yea higher than Riboku's imo. I think there will just be a substantial experience gap between Riboku and Kouen.