Amigo ATC,
You ask "With a compulsory, non-negociated increase in compulsory working hours of about 50% for Spanish ATC (believe me, it's true) and a salary cut of around 50%, how could Aena's managers not foresee that the discontent of the ATC workforce would cause a noticeable decline of service quality?"
I put it to you that knowing full well you have for several years been paid well over the going rate for controllers internationally, you should have foreseen that one day this situation would be rectified, and rightly so.
Whatever difficulties you may think there are to being an air traffic controller, it is no more difficult in Spain than anywhere else, you don't do a better job of it in Spain than anywhere else, so why should you be paid more in Spain than anywhere else ?
I have yet to hear you or any of your colleagues and supporters make any kind of attempt to justify why spanish controllers are worth four times more than those anywhere else.