well yeah, "rammus counters yi" does not mean you can duel him at any point of the game....it just means he cant dive anyone simply cuz he'll get taunted and killed. And in team fights you're a serious threat to him until you taunt somone else, so hes not even going to bother to help until you blow your cc. Thats what makes rammus so strong againt yi(until he gets qss ofc)
if you wish to counter yi, simply play glass vi, xin, rengar anyone that can blow up him...yi is exremely squishy, and it'll come to a point he won't be able to 1v1 you until he gets someone on his team to cc you(since you're pretty squishy too but have cc) ...but ofc it'll still depend on his skill to dodge and block ur spells effectively.
I personally don't think it was early game if you said he killed you with sated, it would mean he either real fed up or its no longer early game.....rammus is a real threat early cuz of his ganks....not safe jungling.... you should try to use that if you didn't.
anyways.....good luck