In addition to his lack of charisma and no apparent sign of possessing any bollocks whatsoever, it's the baffling logic he employs to manage the squad. Certain players will be used mercilessly over and over again, no matter how good or bad their performance is.
That in itself creates a huge problem, already there is no real threat to their position as they know they will always get 90 minutes or close to it.
Then you have the younger players or new signings, who all seem to have to fight with eachother for game time and can be frozen out for 3 months after 45 minutes of football. Despite it being their first 45 minutes in months, so already their is no rhythm or match practice.
We saw it with Alena this season, Malcom was grossly mistreated and really the bulk of his appearances were in desperate situations with injuries or scorelines. There is no continuity with Fati,Dembele,Perez, it's a russian roulette to who makes the match day squad. Again, perhaps a less than perfect appearance will see them discarded for months. So when called upon they are lacking match practice and rhythm.
Other genius moves, like leaving the second choice LB out the squad for a game only for their to be an injury to Alba, so now your first-choice right back goes to left back and the guy you said is now a midfielder and not a right back, has to play right back.
I feared at the start of the season that Valverde would swap the failed Coutinho-Suarez-Messi frontline with Griezmann in a like-for-like and so it proved, it was too much to ask that he'd might of had time to plan a different approach. There is signs of evolution, tactical awareness, in game management with this management at both board level and pitchside.
It's always a bit risky having a manager in charge of a squad, who was a much worse player then the players he has managed and has won minimal silverware also in comparison especially at your big clubs. The only way that ever works, is if he has a character that demands respect and has some vision of how they want to set their teams up, e.g Ferguson,Mourinho(in his prime), Klopp and with players who were successful like Guardiola & Conte.
Valverde possesses neither of those traits, he is the epitome of mediocre. No club who has any ambitions to be one of the best sides in Europe would even consider him if he became available.