Untrue, Xabi often played as a holding midfielder (or a "6") after he left Liverpool. While he started out in a 4-2-3-1 at RM, later he played as the "6," and he exclusively played this position in the 4-3-3 system Pep Guardiola played at RM and Bayern. It is true that when he was playing alongside Mascherano in a 4-2-3-1 system he played the more creative role, but that wasn't always the case. What was the case is that while at Liverpool he always played as part of double pivot in the 4-2-3-1 system. If that is what you mean, then just say it and don't refer to some "effusive" Xabi position, because 1) Xabi played different positions and roles during his Liverpool and later career, and 2) Xabi definitely played most of his career as a holding midfielder, which is a type of defensive midfielder, or a "6." But even if playing TAA as part of a two-man pivot in midfield is what you meant, I don't think even that will really work for TAA with the other midfield players we currently have (and likely will have for the next several years). The problem is not that TAA wouldn't necessarily be a good creative partner in a double pivot in a 4-2-3-1, but rather that this would negatively impact a number of other players, that are arguably as creative, if not more, than he is. Who are the other midfielders that we would put next to him in a more defensive role? MacAlister? Szoboszlai, Gravenberch, Jones, or Elliott? Arguably the only current midfielders that would naturally fit into a more defensive role in a two-man pivot would be Endo and, potentially, Bajcetic. Were we to actually switch to a 4-2-3-1 and start playing with a double pivot, I imagine that TAA would have to share the more creative midfield role with MacAlister, and possibly also Gravenberch, Szoboszlai, Jones, and Elliot. I could see Szoboszlai and Gravenberch as more natural ACM which could solve that problem, but then what do you do with Jones and Elliott? I don't think these two would really be able to win competition for places as the ACM, or either of the two wide attacking positions when competing with the likes of Gakpo, Diaz, and Jota on the left wing, or Salah (or Jota) on the right. Plus you'd really like to see Doak be given some time to develop on the right wing as well. The issue, and I think the reason that Klopp never fully committed to playing TAA as a midfielder, is that while he is a very creative fullback, I don't think he is particularly good at judging player positioning when the opposition is in offensive transition (as wingtips noted upthread). The impression I also got when watching him this last season-and-a-half is that I don't think TAA is quite fast enough at collecting and recycling the ball, especially when under pressure in the midfield. Even if he plays as the more creative man in a two-man pivot he still will have significantly more responsibility for maintaining possession and linking the defense to offense. Additionally, any defensive lapses are much more dangerous in the center of the field instead of in wide positions. Here's a quote by Klopp when asked about playing TAA in midfield (and why he wasn't). "I'm not stubborn and don't want to play him midfield, not at all, but I am not part of the discussion. You [the media] can discuss it as much as you want but it will not have any influence. He wants to play and from my point of view he has to be influential and we have to make sure we help him with the positioning. If you want to be good he has to be influential from all different areas because it just makes us better if he plays a good game." (underlines are mine, and here's the link to the original article). Reading between the lines, TAA wanted to play as many games as possible and not split playing time with others, and wasn't he good enough to be fully effective in all aspects of the midfield position, and playing others in the midfield positions made the team stronger as a whole.