No you don't need to be guaranteed an exotic from Skolas every time you beat him... Although I do think you should get a Legendary Elemental Damage Primary drop every time like if you go 9-0 in Trials you'll always get a primary Adept. From Skolas I got Aigus of Kell II Solar pulse rifle and that's it no other drops.
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After the update that took away the burn on skolas I bet only 10% of people that play destiny has beat skolas probably less. what other game out there is this hard and time consuming for crappy rewards