BTW.... understand from all here that he's best position is Left midfield/wing..... he's gonna find it hard to oust Kewell especially as Harry is finally coming good. Would be a shame if after all he hype, he doesn't get a decent shot.... Would be a greater shame if Harry had to make way..... Wonder if Rafa has any other plan to integrate both of them in the same team.
If we were only to play local competitions, the problem you describe would be real, but given the amount of rotations Rafa is doing (and quite succesfully) I think he'll just use this two very good players with different features, depending on the game. There are leftbacks who can be beaten easily on speed -> Mark Gonzalez, he really makes havoc. If you need a dribbler and you have no space to run because the opposition is very deep -> Kewell.
In fact, if we buy a RW, you might also say that we have a problem with Sissoko, but with the amount of games we have this seasons, it's necessary, now we're deep, and we're quality in that depth, which is nice.