Linking your game to Steam does nothing for this game. You can't even see your Achievements in Steam. I don't know if linking only allows Steam Logins, but I will say that Steam does frequently have issues when trying to log to this game through the Steam portal.
I'm not a steam user myself. I do know that linked steam accounts can still be played from the eso64.exe file the eso launcher uses to play the game if you wish. Steam purchased versions of the game don't have that game file or some others also.