It is well documented that Giles only features when bowling over the wicket into the rough (as you've highlighted) and against left handers. He is really pretty mediocre at best at test cricket. For one, he should be bowling around the wicket - the footmarks are the reason he doesn't so the pitch is as much a problem for him as any RH off spinner. Now of course, there might be the odd exception who comes along once in every ten years (maybe Panesar, I don't know) just like a batsman comes along who can play the late cut.

And if, blocking up an end is the 'art of off-spinning' then it is well and truly dead. Ern is right.