I think you have hit the crux of the discussion mate (as ever, your observations are always good to read even if I don't always agree)...it comes down to whether we will have a system which accommodates a player of this type, a sitting CM so-to-speak. My feeling is that Poch is building a side and system which does not necessarily have a 'specialist' of this nature, instead expecting fitness, intelligence and mobility to dictate the situation. I believe he is very happy with the terrier play of Mason, the slightly calmer but aggressive play of Bentaleb, the fact that most of the time one sits if the other ventures, and that when the balance and work rate of the team is right, we do just fine. I personally feel that a specialist CM of the nature you are discussing will not happen under Poch.
I think most teams are moving away from players like this anyway, as having such a limited destroyer in midfield limits attacking play. We saw under AVB how mundane the play is when you play specialist defensive midfielders. You're effectively narrowing your attacking potential and outlets and the only way you can make this system work long-term is by having some ridiculous beast in the team like Bale who hammers in goals from all over the place out of nowhere when you've turned the game into a midfield slug with few scoring opportunities.
I do not want to return to the sight of Capoue sitting just infront or in line with our CBs, getting the ball, looking up, and passing it backwards or sidewards, because he's a DM and doesn't have the necessary skills. And let's get it right first, a DM who is also good on the ball is so rare only the top teams have them as any such player is going to go for a ridiculous sum.