This is all true and we have to wait how Joan does the rest of this season
But the question is will LDF start him even if he performs really well in the UCL. From his comments, it seems more like he chooses to stay loyal to Unai because he did well on Euros
Joan is gifted with more physical advantages than these keepers and on top of that he is also fantastic on ball. He is incredibly quick, his reflexes are unreal and honestly there are very few flaws to his game so far. Normally he should develop into a much better GK than Simon or Raya
Unai should be undisputed number one in the World Cup barring a catastrophic performance.
Valdes did much better in 09/10 than Casillas and was rightfully benched for Iker. It is the nature of the NT football that is vastly different than club one. There is a reason this loyalty is universally agreed with coaches. Joan won't have time to build a strong connection to this squad and to fit in.
The question should arise after the World Cup, and if Joan don't get a serious look along Raya then there might be an argument.
So far Simon is a critical player for Spain in the 2020's and is just entering his prime, Joan is a pleasant surprise for us but there is no need to be mad on his behalf for such NT decisions.
A big part of getting number one in NT is circumstances. In 2008 Neuer was essentially 5th GK for Germany, and it looked he won't be more than 4th option in 2010 after Lehman's retirement. Timo Hildebrand turned irreversibly shit after Valencia move, Enke took his own life (rip), Coaches realised Wiese is mediocre, and just before 2010 Adler got injured and Neuer became no1 and rest is history. OTOH guys like Reina, MATS and VV waited their whole career for such opportunity.
If anything, I am glad than Joan gets proper rest during international break, I would hope rest of Barca squad to follow.