Too lazy to pick a pic
Besides, I think he's the only trainer worthy of winning the Alola League, although you can make a case for Gladion to be just as worthy.
Honestly, the only point Alola always made it's anything it's possible. I don't think Ash will win simply because it's tradition. Obviously there's a first time to everything, but I don't think it'll be now.
I highly doubt Meltan is Ash's ONLY power up he receives before the league (not counting new Pokemon attacks). It would be unfair to Ash if the only power up Ash gets before the league, is a Pokemon that can barely use any Pokemon attacks (and is simply strong enough to somehow participate in the league). Everyone else is getting new Pokemon as well as Z-moves. I do agree that yes Ash is MORE advantaged then his classmates, but I find it hard to believe that Meltan was Ash's last "power up" especially if we consider Gladion/Hau might have some power ups, I just don't think "Meltan" really fits here except for maybe being good against Lillie's Vulpix or potential "Ninetales" for being completely super effective against it (especially ALOLAN Ninetales).
Ash already have more z-crystals than all his classmates and 5 usable pokemon. While I think he's done for Z-crystals and another evolution could still be on table to him, he's the last character who actually need some boost. Assuming everyone will have a z-ring by the league time, if only to don't job fast at the first round, the classmates and Hau are the only ones getting power ups. Despite the fact Ash could use new tricks against Gladion and/or Guzma, but I prefer a new improvised move than simply depends on z-moves (it could not happen, anyway).