I find it very hard to believe that Harry does outright stupid things like not play Bale in his best position for no reason. To assume Harry can't see stuff that a bunch of dudes on a message board can seems a bit silly.
We've seen repeatedly through the season that while people say we have a great squad, that is only true up to a point. Niko and Gio sound good on paper, but put them in there and they clearly come up short. Some, not necessarily me, might say the same of Defoe, Sandro, Bassong, Corluka, Saha, Cudicini and others at different times. So thinking it's a matter of just "slotting in" these players like it's Subutteo seems a bit simplistic. You also have the issue of how players are - mentally, physically, in training - behind closed doors. Harry might take one look at Gio and think there's no way he's playing even if a certain slot seems right for him.
Finally, we shouldn't forget that it's not as though Bale is useless in positions other than the left wing! I can't remember for sure, but I presume his shot that hit the bar last night came from a move where he was in the middle or on the right. And he always has the option to suddenly pop up explosively on the left just as the right sided defenders have forgotten about him. It's not all bad by any means.