He doesn't have flair imo. He has passing ability, but that is trimmed off by poor and/or chaotic movement around him as is the case with the technical good-passer midfielder who lack 1 vs 1 ability.
Under Koeman, the midfielders who can make the best progress are box to box. Players who combine defensive output like tackles, interceptions etc., with shots and goals at the other end. Koeman's style is direct, no wonder he spent some years in England, I can see why teams there gave him a shot. Players with a good understanding of possession and players who are comfortable dictating the play in more neutral build-up areas will suffer or at least they won't develop at a fast rate. These are CM types, like Pedri. No wonder he instructs the CMs to go up and act like AMs. The CM position is a bit lost on Koeman as is the role of controlling the flow of the game.
Pedri will never be a world-class AM or a box-to-box, he lacks some key athletic abilities that would allow him to quickly appear in the box and score many goals (for midfielder standards). He is a CM. And would suit a system where more control is given to the midfield. This is imo the weakest part of Koeman. He seems to not have a clue how to set up a dominant midfield in terms of possession. Our games look like roller-coasters, often with weaker sides dominating us in midfield.
This is entertaining sometimes, and competitive, but games vs Getafe and Granada should be one-sided when looking at these teams and Barca. They are so competitive and end to end because Koeman sucks at setting up a controlling midfield. He pushes so midfielders so high up that the midfield is under-manned and weak in support.