Eh, this is really only true in theory, tbh. Fact is Theo is a more effective player offensively than Welbeck. If Welbeck could add more goals and assists to his game, yes, he he would indeed be a better player than Walcott. Anyways, we need to count him out until at least March this season, we can't rush him back into action like we did last season, or else the vicious circle of injuries will just continue.
Iwobi is an ideal modern winger in a combinative style like ours. He does come central a lot, but that's one of his great virtues, he combines very well. Actually I think the real question is, if we have a traditional striker playing (like Welbeck, Giroud, or Lucas), and Theo out, who plays on the left and who plays on the right with Alexis and Iwobi? I actually think I would go with Iwobi on the left and Alexis on the right, because when Alexis on the right it tends to force him to be a bit more creative and less predictable, and Iwobi's strength is facing the game, combining, and making decisions with the ball.