Zidane was rubbish at Castilla, it's pretty much certain that his time as Ancelotti's assistant manager did more for his development and ability to handle RM's first team than his stint at Castilla.
And, while they haven't been 'better coached' this year, Zidane is on the cusp of 3 consecutive CL's and 3 successful seasons. He brought RM back to within 1 point of us in 2016 after Benitez got fired and we had a HUGE lead in the league. He won CL and Liga last year. Only this year in La Liga has he truly underwhelmed. CDR is irrelevant across all seasons because it's clear without a shadow of a doubt that RM don't give a flying fuck about it. Their mentality is basically if they can win with 2nd string players then good, if not, who cares.
He has been quite lucky, but a huge part of that is the team dynamic built by his presence. RM feel like winners, believe that they are winners. They find a way to win in CL and never truly collapse like Barca did vs Atletico, PSG, Juve, and Roma. That champion's mentality has taken them farther than Zidane's tactics.
In an ideal world Xavi would become assistant manager for the next season, and if EV doesn't bring the performances up to par, takes over for him in 2019/2020. If you read any of the Xavi interviews I posted a few pages back you'd know his footballing mind is where it needs to be, the only thing missing is acclimating to the rigors of a full European season as coach and handling the motivation of the dressing room.