It is not a handicap but these players are all skill far from refined like Xavi. They are learning and playing of off each other. It does have its disadvantages because a a bad day for someone like Xavi means he isn't functioning at highest level, but a bad day for a youngster means its disastrous, just like Di Maria.
However this isn't an excuse, in fact the only excuse is that we are unlucky to be in the same league as Barcelona. Full stop (trademark: Beast). There is no competition, you team is superb and that is that. Sitting 4 points behind your means Mourinho has done an incredible job with a new team or La Liga is so shit.