I'm not having a go at you here or anything but honestly, do you really believe Valverde is the one who decides Messi plays at RW?
I guess it is most definitely EV who lays out the principal formation.
We all know that the right expression is "Messi starts from the RW" but that in itself influences how the midfielders are spread and never forget that Barca traditionally had good attacking RBs, which Roberto is not and Semedo just could be.
Ideally Messi should be a false9 creator & scorer, just as @seghei says, regardless his age, and at the very minute it would happen, the formation and matching tactics would change so, that the right side wouldn't be empty anymore. Obviously for a change like that Suarez would need to go and that is the point where Messi's role comes in, but I'm not sure it works as easy as many imagine that.
I don't think he openly has pressure on EV to play his buddy all the time, rather - I'm saying it without having an insight - I imagine EV knows that without words being spoken and acts accordingly.
You are damn right that probably EV has no respect from the seniors, which unfortunately works as a rolling stone, because it automatically results the younger ones also to disrespect him.
I think, just think, that the entire locker-room plays the theatrical play, as if they would hear and listen to Valverde, but in reality they simply ignore him. Of course it doesn't mean that Messi is the one making the actual formation, and I also seriously doubt that EV is actually listens to his "advises".
I think EV was busy with screwing up the midfield and giving bad advises to the defenders last season, while he left the attack on the "known" formation of Messi and Suarez, regardless if Coutinho or Dembele or whomever was the 3rd attacker.
The situation has changed considerably by the arrival of Griezmann, because EV knows he will not allow himself to play yet another star out of position, unless luck stics to his side.
I think the team and EV is in the PHASE of a faint hopie that it might even work with Griez on the left, but by now most of them know it will not work, so that's why we hear faintly unsatisfied voices from inside.
I'm also just guessing, but Messi's important role is not in making the actual formation, but rather if he could be able to persuade his physically rapidly ageing friend to accept the bench.
Nevertheless I'm on the opinion, and that's just an outsider thought, that there will be unexpected changes very soon, but still it is the coach who makes the formation and not the GOAT. Probably everyone silently know his opinion, that they consider to be better than Valverde's and it will lead to some unexpected havoc, soon.