Actually in modern football, no 9 has defensive responsibility. He need to be able to pressure opp cb or drop off depending on the instruction. Btw Ronaldo is atrocious defensively, all team that face Real, always attack his side. There is a time when having a no 10 that is good defensively is important. Playing against Juventus is a very good example. Oscar was brilliant last year in term of "shutting down" Pirlo. I really doubt mata can do the job as good as oscar.