The full Moon doesn't really give waterbenders any new abilities,
The moon is the source of their abilities. No moon (like in final of atla book 1) means no waterbending. Full moon means they are at the apex of their power.
Yes, I know. I think you overlooked a couple of the words I wrote there. I said the
full moon doesn't give them any
new abilities beyond what they always have from the moon the rest of the time. As you say, the full moon simply makes their existing powers stronger. Therefore it follows that it's theoretically possible that a particularly strong waterbender could be as powerful normally as other benders are during a full moon.
Both Katara and Hama who were master waterbenders required the full moon to bloodbend. Why were Yakone/Amon/Tarrok were able to do it out in the sun? There is no established precedent of genetics giving unique bending abilities other than determining the type of bender they are especially since we have an example of twins with one bender and one non-bender.
Apparently there is now. You can argue with the explanation they gave, but they
did give an explanation: they didn't need the full moon because they were exceptionally powerful, and that makes sense because all the full moon does is amplify waterbending. The only question is
why they were so exceptionally powerful.
Combustion Man's abilities seems to be due to his unique control of the chakra on his forehead and the damage to that chakra via boomerang proves ultimately to be his undoing.
I have acknowledged in previous posts that I am aware of that. But a single fact in isolation is not proof of a blanket theory. If there's only evidence of one person having such a connection, it's only evidence about that one person, not all people. So by itself it's not probative of anything. You have to consider
all the evidence. Even if Combustion Man had tapped into his
anja chakra somehow, that does not change the fact that Aang was able to become accomplished in three bending arts without even knowing what chakras
were, and that changes in the status of Aang's chakras had no effect whatsoever on his bending ability, only on his ability to enter the Avatar State. The evidence we have is that knowledge of chakras is an advanced and possibly unusual discipline, and one that's normally more connected to spiritual enlightenment than elemental manipulation, except maybe in one unique instance.