At +2 with no boosting item, Rock Blast always KOs both Chandelure and the genies in two hits. At +0, it always KOs 252 HP Chandelure and 4 HP genies with two hits. If the genies are under a sub at >70% health, it requires three hits to KO, and if they have a Charti Berry at >70% health, it requires three hits to KO. However, the really important calculations, 252 HP Chandelure and 4 HP genies, are always KOed by two hits, so it is absolutely a viable option.
X-Scissor actually only does about 33% more than Rock Slide to Amoonguss, so it's not really that much more useful except at +2, and even then, X-Scissor does 71% maximum, so it can still easily Spore Crustle.
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Currently out, college apps are poison. C&Cers, contact me if you need any help with anything important. Sorry!