1. He is 5star 

2. He is not a damage dealer 

That said he will do decent damage with GS in CB, and he is great for CB.  So 6star and masteries and you are all set.

Adding onto what trips said, build Vogoth out with big HP first and foremost. Will help teams in a lot of content with sustainability. 

Vogoth is a healer, not a damagedealer. He lands a leech debuff and heals the teammembers with his passive when attacked.

To make him survive at CB, he needs to be 6* and have Giantslayer masterie, so he can heal from his own leech. The damage from Warmaster/Giantslayer is taken into account for healing with the leech debuff.