You gain S grade expertise in c3 at level 67. 🙂 And yeah, you can buy S set in the shop and killing Pytans with any class shouldn’t be a problem. Especially if you are a titan or something like that. Mage for example (I play spellsinger) can sleep mobs and kill them 1 by 1.
It is not that you do not understand, it is that you do not even question.