From a pure damage perspective, Riven will generally do more - she has a lot of burst potential with her ultimate, and a lot of staying power with her shield. But the kit of Irelia is very deceptively strong - if she's sufficiently tanky, she's incredibly difficult to peel off a carry, and since the lategame is usually defined by whose carries stay alive, that makes a lategame Irelia extremely difficult to deal with if she's farmed/fed. So in most situations, Irelia would tend to win out, but it'd be heavily influenced by team comp - if the enemy AD carry is well protected, Riven may be better just for her raw damage if Irelia is unable to reach/kill the enemy AD carry. I feel Jax and Olaf are almost kind of an intermediate step between the two of them - not as good as sticking to an enemy AD carry as Irelia, but higher damage threat. All are strong lategame fighters.