Absolutely nothing to do with either of them not being good enough defensively. Instead it's completely to do with the fact our style has risk. If the press is broken our back 4 is called upon, sometimes it fails but no system is perfect though that aspect will continue to improve with time.I actually agree about them to an extent with Mason and Bentaleb. Both players are good, but together they leak fast breaks like a sieve. Mason is good going forward, but not very good yet at breaking up attacks, and I think that he'll be the one likely to be on the bench next year, of the pair.
I like his commitment, and his attacking instinct, but defensively, he's not that great. He tackles, but the downside of tackles is that if you miss, you've taken yourself out of the play and given space to the opposition. He does that a lot more than I'd like.
That problem is why Dembele's been playing as a #10, and although the tactic is working, if Mason and Bentaleb were better defensively, we wouldn't need to do that in the first place.