I don't think that's really true, though. We just didn't have options on the wing so when Theo got back from his injury in the Carling Cup he played Theo on the wing with Giroud at CF (obviously, as he can't be moved wide).
In that United game he did in fact play up front as the primary CF as I recall. He was absent in that game and then Welbeck was given most of the opportunities after, understandably.
Pulling the plug on the Walcott at CF experiment isn't really an accurate characterisation, though, if Walcott didn't get injured when he did/other wing options + Santi (forcing Ramsey to go into the middle) didn't get injured when they did, I'm sure he would've continued with it, but in that period we were so short on options you pretty much had to play both Walcott and Giroud, with Walcott on the wing. Walcott was subsequently shit on the wing, got into very poor form, and that was that.
Aside from leaving us short on the wings, tbh, Wenger was guilty of not giving Walcott another extended run at CF after the promising spell in autumn. Walcott's shit form on the wings made it hard on him, tbf, and so it was understandable he became 3rd in the pecking order with Walcott and Giroud, but a manager with vision and patience to see out what was a promising experiment would've given Walcott the games Giroud got in the late winter/spring when Alexis came back and Joel and Iwobi emerged.