The point is not to get a manager who is better than Valverde. We can do and still end up with decent one at best. We can bring Quique Setien tomorrow and we'd improve from Valverde, but the aim can't be as low as improving from a tactically weak manager like Ernie.
The point here is to get a top manager. Someone who'd be able to come up against the Klops and don't look amateurish by comparison. And for that we need someone who is 2 levels above Valverde. We have no access to A tier. We need to get a manager from the B tier. Valverde is C or D tier. That's good enough to win leagues by regularly smashing the teams in La Liga, but not nearly good enough for what we want to do in Europe.
The question is if Koeman is tier B, or he is just a new Valverde. We need someone who is at the very least as good as Lucho was to feel a serious improvement from Valverde. Lucho is the benchmark to improve upon in the next appointment, not fucking Valverde.
There is a risk that Koeman is just as Valverde, only with more discipline and tenacity. If he is not a big improvement over Valverde in the tactical area, then he is not the manager we need.