I know Skarm will block a sweep, but as you agree if it is last Pokemon it will beat Skarm.
Yes, but last Pokemon are much more messed up by a lot of other things, so that doesn't really help the problem, it merely moves it over to a different category. Admittedly, Revenankh is pretty good at being a last Pokemon, being immune to Explosion, access to Shadow Sneak before Destiny Bond and generally being a pain to take down. However, Perish Song will now mean Revenankh loses always unless it kills everything before its 3 turns are up. Leech Seed no longer forces it to switch, but to die pretty much (or at least, it will have significantly more trouble...enough for Skarmory to stall it and try to CH with Brave Bird, for one). It can no longer back out of Togekiss, Yanmega and friends.
It is kind of silly to take last-Pokemon into account for everything, considering a last Pokemon is a whole new package. You could mention in the analysis but...I already wrote an article about it, so I'm like whatever. If Revenankh is the last Pokemon I already killed five opponents, and usually when that happens I am already winning.