When serge is good he is actually quite good. But does make errors. He really ought to play a little like doherty/trippier who let people put crosses in and leave it to the centrebacks to deal with them.
Reason why Sir Alex Ferguson said Denis Irwin would have been one of his easier picks for his all-time best 11 at United was reliability. Next to no mistakes.
Aurier makes one every 3 or 4 games. It is always likely. Not sustainable.