Talonflame was consistent the whole way through XY. At no point was it "turned" into a Jobber. In the league it beat Sawyers Slaking and drew with Alains Unfezant. The only official battle it didn't get a loss in was the double battle vs Olympia. And it was never the Ace
With all this Greninja hate, it's pretty clear that Lucario is going to be absolutely despised in a couple years time lol
Tell me: What defines Ace.
Talonflame: Participated in every gym except for Clemont and didn't go down in one without at least taking down another mon (Except for Grant).
Greninja - Only 4 gyms, which one was for Ash-Grenina (So separate from Greninja), needed to be carried by Talonflame through the match with Olympia (Without Talonflame it would have lost), so it only did good in 2 out of its 4 gyms (Ramos and Grant).
Talonflame didn't go down in the league without taking down another mon either.
Greninja only took down Bisharp, who was already weakened by Goodra and Hawlucha beforehand, while Ash-Greninja took down Altaria and Sceptile (But again, Ash-Greninja's wins are separate from Greninja's, since he didn't take them down in regular form).
Talonflame fought 2 legendaries (While Greninja fought none). Fletchinder brought a hit in against Mega Lucario (While Greninja needed its power-up form to bring in hits against Mega's).
Talonflame has had way more impact on the gym run than Greninja ever had, which means that in fact, Talonflame was the ace, so what more needs Talonflame to do for people to finally recognize it as the ace instead of that overrated frog who wasn't that impressive in regular form compared to Talonflame and even Hawlucha.
If Talonflame wasn't the Kalos ace, then Groyvle wasn't the Hoenn ace, simply for the fact Glalie outperformed it during the league and as such was the ace.
However, its hard for some people to recognize that some series have multiple aces
Kanto - Pikachu
Johto - No Ace (And if we need to assign one, it can only be Bayleef for the new mons and Pikachu)
Hoenn - Gym run ace: Grovyle. League ace: Glalie
Sinnoh - Infernape
Unova - Krookodile/Pignite
Kalos - Gym run ace: Talonflame. League ace: Ash-Greninja (So not even the regular form, since even in the league regular form was outclassed by Talonflame and Hawlucha)
Alola - Lycanroc (Performed way better than the rest of the mons).