Valencia the football team did not think that when they sacked him!
he lost the dressing room - the mighty striker Joachin stated we listened to RK instructions as we were in relegation trouble went out and played the opposite and won games to keep us up!
They where in relegation trouble not due to tactics mate, but due to the fact the the core group of veteran players quit on him, so shock horror according to Joaquim (who btw wasn't a mighty striker - he was an out and out winger) - when they decided to play because they bricked themselves about getting relegated they started to win games again...
Most of the players he tried to get out the side btw, where within a season or two moved out the club and the ones who remained saw themselves demoted - by Emery the current PSG manager
As for Valencia sacking him proving anything, this is the same club that has had 12 managers in the last 5 seasons mate
Oh BTW mate, for further clarity - this is the final paragraph from the articl in the Guardian you have taken your quotes from, which sheds a little light on the picture your painting maybe
Koeman has hardly helped himself, but the real culprit is a club that's never at peace; the Dutchman walked into a viper's nest, where sporting directors and coaches are at each other's throats like a bunch of deranged emus; where, with honourable exceptions, fans are never satisfied; where president and shareholders are always at war, creating tension and instability. As Koeman boarded an empty bus on Wednesday night, the club handed out press communiqués saying there would be no formal celebration. No visit to the town council. No open-topped bus. No silly wigs. No offering to the virgin. And no one informing Koeman. Above all, no embracing of the one thing that could have brought the club together, revealing yet again what a miserable, self-destructive institution Valencia has become, one that's about to put a fourth manager in charge. If they go down many will wave goodbye, but many too will wave good riddance.