I think that this thought process is a fallacy. Who is Giggs going pick over the youngsters? The more obvious reason that they are getting game time is because they are better than the more senior Welsh players who play in the same positions as them - not because they are being blooded or other terms that I've seen used.
Giggs is picking the best players available to him and isn't getting the results or, perhaps, more importantly, the performances you would expect from them.