A pure tank fighter is a wannabe paladin.
Indulge me. I found fighters superior but that was before I knew that FaC only works for the Watcher. Why are paladins better?
Side note: My previous post is a bit from the perspective of "IF YOU USE MY PLAYSTYLE THEN ETC ETC" but I don't think endgame fighter tanks are going to do significant amounts of damage outside contrived situations.
Higher all-around defenses, mainly. Supportive things to do while tanking, to a lesser extent.
It's by a small margin, but I do think that as a pure 100% tank, paladin pulls ahead and stays ahead.
A lot of what fighters use to tank is based on taking hits and then recovering from them. That's great if you're expecting to take hits, but in PoE, a pure tank looks to avoid them outright.