On the contrary, Ike is not the best character in heavy lag at all, since if you cannot shield, you cannot escape heavy projectile spam (i.e. Pit, Falco, Wolf, Pikachu, etc).Ike is a punisher, he suffers when approaching. In addition, for Ike to hit people, he first has to get close to them, something that lag does not exactly allow well for. Also, if anybody, but ANYBODY is approaching an Ike when he's charging a move, they basically deserve to get hit. His recovery also gets gimped heavily by lag.
On the other hand, you have MK, whose offensive game actually IMPROVES in lag, seeing as how nobody can react fast enough to shield/spotdodge and then punish his incredibly lagless moves. As well, since all of MK's moves chain together, it proves very easy for him to just mash on the A button if he isn't quite sure of the timing, and lag prevents punishment of this. His recovery is too good to be gimped by lag, as all you basically need to do is get to about stage level and use his incredibly broken ^B to go around everything in your path.