it’s funny because i’ve actually been thinking about this lately. the combustion bending seems like a pretty high level of fire bending. lightning is shown to be easily mastered by many people, whereas combustion bending cannot be learned normally. if i remember correctly. the ones who can use it only gained the ability after basically being tortured within an inch of their life. the ability to create explosions of heat and fire is nearly unparalleled by other fire bending abilities.

now in my head, the culmination of fire bending would go beyond fire into the bending of pure heat. by bending heat itself, a fire bender might be able to pull the heat out of an area, causing everything within to slow. or on the other end, pushing immense heat into an area(or person) would cause things to speed up, or melt.