Not exactly Ken, you've completely missed the point. I'm talking close formation here, just like in the video. In all the large aircraft formation I've done I stay in formation, so when my leader rolls left or right I climb or descend slightly so that I can maintain IN FORMATION. Simples!
The operative word in your phrase "I climb or descend slightly" is "slightly". In a large formation of large aircraft the "climb or descend"
cannot be "slightly". If the airdrop formation is 1000 feet (or less) above the ground in a formation of four C-17s, the bottom C-17 ends up trying to "descend" below ground level. Nature has a nasty way of resolving the conflict between granite and aluminum. That's why in those formations, the formation turns are done flat.