I think when you get them all together, they lack intensity through the natural subsequence of aging, and thus fall into playing a game which works around this. If Xavi can solve this and get those 5 all playing with the fitness of 2015 levels then great. But he should also have the hindsight that he himself at the same age had to ride the bench with Enrique as he could not physically bring it, which he noted in interviews how meticulous he had to be with his fitness, diet and sleep patterns at that age to try and keep up.
So to build around a team of 5 players past their physical peak is questionable.
The fullbacks are auxilliary to the structure of the team and have to just assist the basic functions of the team at a decent level. We won CL with combinations of Gio van Bronkhorst/Sylvinho/Adriano/Abidal and Belletti/Oleguer/Alves and would with Alba/Firpo and Dest/Emerson/Roberto too if the spine of the team (Centre mids, Centre defenders, striker+Messi) were at peak levels too. So I wouldn't care to analyse starting Alba and Roberto or Emerson or Dest too much.
But maintaining the spine around Pique, Busquets, Messi, then Aguero as Font mentioned him is problematic. Then if de Jong is not mentioned as a core player, he might as well be sold.
This is how it often has looked, and I say it is because the focus of the coach/the other players hasn't been the right one.
Roberto is of course not essential, but it is essential that his type is valued and isn't instantly ruled out in favour of someone like Semedo/Dest or Vidal/Paulinho.
All five doesnt need to start, Messi+Busquets+Alba are the three best players and the team should be setup to suit them. Pique needs a kick in his ass, but under the right manager with the right surroundings I have faith in him being able to bring a lot still.
Although I think that Xavi should've played a lot more, if he says what you wrote then at least he is very aware of the problem.
I don't think Aguero should be close to be a core player, but I was like Font positive to bring him (probably as a supersub, but he could very well show to be a starter as well)
Yeah I agree about de Jong, and I don't think he is good enough as a midfielder for Barcelona currently, but he has great potential and should benefit A LOT from being under someone like Pep or how I imagine Xavi to be for a year or two.