Analogy time!
If Hama is to Yakone as Zuko is to Combustion Man then WHO is the correct analogy for Amon?
A. a water healer
B. a chi-blocker
C. a lightning redirecting firebender
And as you can probably guess, IMO, the answer is ALL OF THE ABOVE. What we see in Yakone and Combustion Man is the use of a power without the physical expression of it. Yakone doesn’t need to move to bloodbend, nor does Combustion Man need to move; in contrast, Hama and Zuko do need to move to bend.
Amon seems to control the flow of his chi — as healers do, as chi-blockers do, and as firebenders do to redirect lightning (arguably to throw it, as well). But while a healer uses an element, a chi-blocker uses physical movements, and a firebender controls it only internally to form a circuit, Amon has full control no matter the circumstances. He doesn’t need a special movement to resist bloodbending, he can use his chi control internally and externally, and he doesn’t ever draw on any element.
As a sort of side note, I think this reflects that bending and use of chi in their universe aren’t necessarily reflections of pure power. It’s easy to look at it that way, but I don’t think Yakone or Tarrlok is actually more powerful than Katara or Korra, any more than Combustion Man was more powerful than Zuko. They have different understandings of the elements and different expression of the element. Ultimately, I think episodes like “Firebending Masters” prove that understanding is key and that power is not innate.