Well, yeah, he's not going to turn into a great defender. The point is, we should absolutely not be rejecting offensive players because their defending is a little suspect. Other teams don't generally do it, teams that are currently in a better position than us included. Unless the player is just ridiculously hopeless off of the ball I.E Taarabt, then it's fine.
We do not need a team of 11 workhorses. We have plenty of hard-working players in our ranks and our abundant lack of creativity and clinical edge left us with 5 goals in open play after 6 CL games.
Sacrificing a bit of work-rate for a lot of creativity at this point is absolutely vital. I don't know why some people are suggesting that the only way we can be successful is by having 11 willing runners. That's obviously not true. In fact, it's proven to be incorrect by a whole host of top clubs every single year.