Your gear is more than adequate for Kologarn - it's considerably better than mine was when we first killed him.
I suggest it might be a few things. Are you keeping debuffs up on him? Are you swapping tanks at 2 debuffs? Are the healers responding well to the tankswaps? Are the healers coping with the combination of raid damage and tank damage (i.e. they're not forgetting to heal you, right? ) It's a tough fight for them at first while people are learning.
Without a parse of what's killing you it's tricky to diagnose. But on the face of it there is nothing preventing you from tanking that boss successfully.