Stamina is absolutely vital for any players who use playmaking. For inner midfielders it's not a secondary skill, but a primary one together with playmaking. One of the most common mistakes by playmaking trainers is to slowly increase stamina for their players. Playmakers with anything below solid stamina are a waste of resources in a league or cup game.
If a player does not have enough stamina, a serious drop in their playmaking contribution will be noticed, particularly during the second half of matches.