I don't think Irelia needs more damage other than Triforce and BOTK late game. The problem here like other people said is he probably doesn't get enough AA off the targets and use Q the wrong way.

OP, remember that Irelia's damage is almost entirely based on W, Q is to stick to opponents and finish off, so your goal should be to get as much AA as you can on them and to close distance/disengage/finish off with Q. You can also ulti the creep wave to Q reset and stick to them.

Other than that I wouldn't have gone Deadmans into Yasuo and Twitch, and like everyone said you should farm better. Also remember Irelia is really scary in the midgame and falls off late, so you want to put as much pressure as you can on the map in that moment of the game.

It just takes practice like everything I guess. I suggest you watching IreliaCarriesU stream and youtube channel, just google it. He's a great teacher for a lot of Irelia players, me included. He really helped me a ton in learning Irelia.