who told you both of them fall off late game?
Irelia is somewhat weak in lane after all these nerfs, but still she can manage to get some farm and wreck your carry while you can't really CC her in midagme. She does have a decent lategame, dependant of how you managed the previous phases.
Wukong on the other side, just does have a niche, he does have a hard time in lane cause he doesnt have sustain and his mana issues are somewhat big. However, he shines in teamfights no matter what, being at all times tanky.
Wukong for fun, Irelia for a win game.
Why not both? :P