Comparing Koke and Gundogan is very interesting, both are similar players and are at a similar level of ability. Gundogan functions better in the Xavi role but Koke is the more versatile player all round.
Koke is the more capable player physically and defensively under Simeone's tutelage over the years. He's also infinitely better with set piece deliveries and the better final chance creator in general averaging 3.7 key passes per game this season and having awesome assist stats yearly from various scenarios despite playing in a defense-heavy team. He can play as a wide midfielder, CM, DM, and debuted at RB for Spain. When he's had the right chances to show it, he's proven that his pass and move game is excellent (like vs. Malmo in the 4-3-3 setup, shifting to CM against Real Madrid in la liga this season).
Gundogan, on the other hand, is more refined technically. He's intelligent and aware in the way Xavi is and his footwork/agility is great for a player in his position. Rarely do you see a central midfielder accelerate at the level a fit Gundogan does. He's like a German version of Thiago (or vice versa since Gundogan came first), the difference being his German engine/dynamic ability compared to Thiago's flair.
Gundogan is definitively better for a team like Barca but when comparing the two in caliber they are very level.
