I put in 8 hours n still can't get skolas beat for what crappy etheric light, weapon core and armor core get real bungie. Skolas should drop exotics every time with 50% gjallarhorn drop for how long and hard it is. I'm done with skolas tell it gets updated again..
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.