Avesta isn't a cheater. A good majority of his tactics are sound and do work or did when he used them (some of the videos predate nerfs, ex: ODS and sleep resistance, I believe). While a good dose of skepticism is healthy, without any proof, it's just skepticism. Nothing about him or his strategies leads me to believe he cheats in the slightest. I've witnessed a RDM solo Amikiri once before and it's an amazing sight. A single player accomplished what well-equipped parties have failed to do and it was without any hesitation. He had it all strategized and timed out. It was almost too perfect, but if someone is smart enough and quick enough, I don't think it would be stretch for the common player. A lot of the game mechanics are very simple. Sleep lasts a predertimed amount of time and so do a lot of other spells. SS, Phalanx, etc. all absorb a certain amount and if you can get a decent understanding of how long they last versus mobs attacks, you can know when to recast. My point is this, with enough preparations and good strategies, almost anything is possible. Just because you think it's not, doesn't mean it's not. You have to realize how many trial and error runs that went into each and every video as well. Just because the final product went smoothly, doesn't mean there wasn't a hundred more that wound up as failures.
Just my two cents, take it or leave it as you wish.