I disagree
To begin Infernape has been getting stronger after DP as it was stated in the last episode. And Blaze is an ability that makes sense with Infernape's nature species having a wild-like personality.
It's an earned power up that exists within Infernape's ability and it took Ash a long time and effort to master it. It was established in early DP and developed throughout the latter. BP is just bond of friendship asspull that was barely developed and it was established towards the end of XY without proper development. Makes no sense. The explanation for it that it is a rare phenomenon that comes to happen every 1,000 years or so in short: an asspull.
I still think Charizard is stronger than Infernape but saying he wouldn't give him a good run for his money it's not true.
So? Ash journeyed with Charizard way before Infernape's introduction
and had it put in longterm training after, which it had been doing for multiple series/generations. Enough context (some outright mentions by Oak himself) has proven that all of Ash's Pokemon continue training/getting stronger at Oak's lab while Ash is traveling elsewhere, so that doesn't mean much.
Greninja's power is also earned, technically, just via a different way. It also took Ash a lot of effort and a long time to master Greninja's power as well, and the development with that was
much more intense, physical, intimate, and difficult than mastering blaze. You've also forgotten that Greninja and Ash were connected ever since it was a Froakie too; the bond hints came way before Olympia's premonition. It wasn't a last second asspull. A full out comparison between the two abilities is also nonsensical because blaze can activate in any evolved state, while BP is akin to Mega Evolution in requiring a fully evolved Pokemon to use at all.
It certainly is true. If this were Flint's Infernape, who OH-KOed Ash's Infernape with a single Mach Punch (lmao), which would never happened if Charizard was in that fight, then you'd be right. Ash's Infernape though? No. Especially with it's extremely lame/impractical moveset, which the Moltres episode highlighted. Charizard has the type advantage, but more importantly, aerial mobility that Infernape has no answer for whatsoever. Ash's Charizard is also notably very fast and agile, as shown being able to outspeed Iris's Dragonite. Dragonite's species is stated/documented to be able to fly faster than the speed of sound, and Ash's Charizard had no issue keeping up and even instantly moving up behind Dragonite. Like Pikachu's Thunderbolt against electric types, Infernape's Flamethrower will be useless against Charizard, who will either negate it with its own Flamethrower or repel it like Flint's Infernape did when Ash's used flamethrower on it. Dig obviously won't be useful either, period. Infernape isn't landing any Mach Punches (even if it did do you really expect it to do much damage or Charizard to keep getting caught by it?). Flare Blitz won't do much either. Infact, at Charizard's level i'm sure it could literally block those attacks with its bare hands, like it did Articuno's Steel Wing and other physical attacks from other Pokemon throughout the series.
So there's no reason to believe Infernape would give the immensely more experienced Charizard a "run for its money".