^ What the hell am I reading? S
Some of you are seriously overestimating the Kalos team...
Kanto: Impossible to determine.
1. QF: Ritchie v Assunta came down to the final Pokemon. XY Ash would easily defeat Ritchie and therefore likely defeat Assuna.
2. However, we have no idea of the other semifinalists. For all we know, they could be high-level trainers like Paul or Tyson or Alain.
XY Ash reaches at least the semifinals, but it's impossible to say if he goes further.
Johto: Circumstantial
1. Leprechaun is marginally better than Harrison (60/40 he wins). However, Johto Ash had Snorlax, who did the heavy-lifting in defeating Hypno and Steelix. Charizard v Blaziken was so brutal that even with PC healing, Blaziken was too injured to be in the next round. So bringing down Blaziken depends more or less on the frog. XY Ash > Harrison, but let's not pretend it would be an easy battle.
2. Harrison v Jon Dickson went to the final match without Blaziken. The implication was that if Blaziken had been in the match, the battle could have gone differently. JD v finalist also came down the final Pokemon. So assuming JD used the same team in the semifinals and finals (which is a huge assumption), then with some mental gymnastics:
XY Ash > Leprechaun >/= Harrison (w/Blaziken) >/= JD > finalist
In this scenario, XY Ash wins the league. All bets are off if JD, or even Harrison, used different teams in the finals and semfinials, respectively, than in previous rounds.
Hoenn: Very difficult to predict
1. Tyson > Leprechaun, and the Kalos team barely got by him (maybe Ash could have won 6-4 if he switched). Zero-true-losses Glalie neutralized the Sceptile. Swellow hard carried by defeating Hariyama, upset win over Donphan, and cracking Metagross' armor allowing Grovyle and Pikachu to bring it down. Ended up being so close because Pikachu went all-out against Puss in Boots. So it's not even certain XY Ash wins over Tyson; it'll come down to some Pokemon stepping up and the right match-ups.
2. Tyson had to win five consecutive full battle to win the title. That's impressive. It's also possible he was using some of his reserves in the later rounds, which means all bets are off over the quality of his opponents.
XY Ash could win the Hoenn League, but he certainly would have to rest the Kalos team after two full battle rounds, and rely on reserves.
Sinnoh: No
1. Umm...unless Rain Dance clears away the Toxic Spikes, or Smogonbird does kamikaze Flame Charge runs on the battlefield, good luck on getting rid of that entry hazard. Paul's Drapion would probably mop the floor out of Smogonbird and Lucha like it did with Torterra, Buizel, and Staraptor. Depends on Barney or Dracula Otachi to be Gliscor and get rid of it. XY Ash needs to switch-in-and-out the frog to hard carry like Infernape.
2. Anyway even if XY Ash defeats Paul, he's losing next round.
We all know Trollbias' team was Darkrai, Latios, Latias, Lugia, Arceus, and Barack Obama. "Now I am become Death, the destroyer of Worlds."
Unova:Likely
Even if it was a team of Eeevolutions, Virgil was highly competent. I give XY Ash a 60/40 chance of defeating him, and then going on to take the championship.