I don't think refereeing is corrupted to Madrid or Barca. There used to be corruption in La Liga a long time ago as you mention but we're in the modern day, that kind of stuff doesn't happen any more, there has been no evidence to suggest adulteration of games since the 2000s.
Just because money hasn't exchanged hands that doesn't mean the referreeing isn't corrupted.
When you have a system in place where the La Liga president always supports Madrid and you make sure the vast majority of referees support Madrid, there's no real need for Madrid to dip in to their pockets is there? The corruption and bias in their favour has been implemented for them, from the very beginning, FOR FREE.
Those that think that a referee that supports Real Madrid won't subconsciously benefit them in a profession that is so largely reliant on interpretation are wildly wrong. Anyone that has an emotional attachment to anything will subconsciously be favourable to that thing. That's a human fact. These referees are not able to defy the laws of nature.
And if you think Tebas is bad, there was a Real Madrid supporting La Liga president who openly said " AS LONG AS I AM PRESIDENT, I WILL MAKE SURE BARCELONA DOES NOT WIN A TROPHY. " That is outright, undeniable evidence of a system put in to place to favour Real Madrid and hurt Barcelona. Where was the court case for that one? Yet another one who needs to testify in court now, it seems.
And then you have the Classico as early as 5 years ago when a linesman came out and said he was asked to favour Real Madrid. But Franco's club gets that completely washed away. Where is the criminal trial for that one???? Seems to have been buried away. Contrast it to the reaction to the Negreira case and you realise that nothing has changed today from the 2000s or even Francos time himself.