Thats my biggest gripe with your opinion, its all just assumptions while being incredibly self assured.
That's because of patterns in everything in life.
If stats say that 90% of biggest La Masia talents never reach Barca's level, then when we will have a new shiny kid in 2025, what do you think that my first reaction will be?
1. Omg, he is the next big thing
2. Or, he has 90% chances to fail?
Now, since each case is unique, then you have to assess each single player based on 2 factors:
1. 90% of his peers will fail
2. Assess his skills
If a certain kid looks way better than all other similar cases during years, then his chances go up to 20-30% to make it.
If he looks the same as all other similar talents through years, then it is fair to rate his chances at 10%.
If he looks even worse than similar talents over years, his chances are even lower than the average (lower than 10%).
Of course, here and there some player will always break the odds and maths.
But in general, if you'll play the odds game, you will be right in a vast majority of cases.
Stats and history exist for a reason.
Regarding Xavi, let's take a look at the Barca's coaches in the last 20-25 years:
Pep, more leader than Xavi
Rijkaard, more leader than Xavi
Lucho, more leader than Xavi
Van Gaal, very stubborn guy in a different way.
Crujff, a leader and a charismatic guy
Who was bad to average at Barca?
Tito, a nice guy
Tata, a nice guy
Charlie Rexach, extremely nice guy, loved by everyone
Serra Ferrer, very nice grandpa who never fights
EV, a nice guy, a pushover
You can do the same for majority of European teams.
Who were the best coaches over years?
Pep, Klopp, Zidane, Capello, Ferguson, Mou.
From Xavi, I am getting Wenger/Tito vibes.
So, you will rarely find nice guys as leaders/coaches of top clubs since they have to make drastic decisions, clash with egos, bench top players.
And nice guys usually aren't good in tough and chaotic moments, in arguing and doing drastic measures.
So, when you ask me about Xavi, when you analyze history, odds, his psychological profile, his friends playing for Barca, a chaotic situation with our bad board and sportung directors, then the odds are astronomically against Xavi.
Again, football and coaching is way more than TikiTaka and nice off the ball movement.