1. Revert, change, is a matter of semantics. He changed the Sith from what they were currently doing (the Ro2) in favor of what he viewed a stronger method.
2. These Sith are not purposly weak, none of them in his era currently have the power to be viewed as a threat except for Cade whom he planned to make his heir. His group contains decently powerful members, White Eyes for example was said by Lomi Plo to be strong as well as the other Sith she encountered.
Talon and Nihl can go one on one with the strongest Jedi we've seen in this series and only lose to a RAGE'D Skywalker, which well almost everyone also does. Had a Sith been powerful enough to kill Krayt, he'd be groomed to do that and take his spot. Really, your blaming the era not producing uber leet people(that we've seen in a 24 issue comic so far) and making it Krayts fault.
3. Betrayal a way of the ancients? The same ones that were Ragnos's sycophants? The same one's that kept Simus a head in a jar alive...and when he died cried out "Oh poor Simus?" The same Sith who challenged each other head on? Sadow added the betraying aspect.
4. Once again, the old Lords don't recognize him...Bane...who himself is a pretender...Nihlius whom doesn't give two shits on a stick about the Sith...and Andnedu...who we know absolutely nothing about. Ok. And yeah he's a self declared lord but every Sith save for Kun, Palpatine and Vader are also. Does it matter?
The point: who cares if he doesn't have the blessings of a bunch hybrids, and anther "pretender" whose stupid rules got broken. I'll enjoy good stories and characters over worrying about "Sith Legitimacy" cry moar jeez...
Actually it could be argued that Nihilus is more Sith than any other as he was the only one to ever totally free himself from all restrictions ( rules, stigma, expectations) and chains. It could be argued that he is the epitimy of the Sith Code.