I think there are only balance changes if your replays are deleted, and so far they seem to warn us about such patches in advance.
He's really interesting. While it's true he's better vs projectile spam than most slow characters (without Revenge he probably would've been the worst character in the game) he's still very, very slow and with a pretty bad recovery. Maybe he's somewhere in mid tier but I don't see him being high tier anytime soon.
Magister did post a matchup chart for Incineroar:
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Winning vs Chrom and Shulk is pretty nice (if true), going even with a bunch of relevant characters is also nice, but he loses to a lot of the meta, and loses hard to Lucina, Olimar, Ness, and Pokémon Trainer, fairly common threats. Still, it's not a terrible MU chart and he could be mid-mid or even high-mid if accurate.
If accurate. A lot of mid tier mains have a tendency to overrate their character, and even Magister himself admitted that we should take it with a grain of salt, so we'll see. I'd be curious to see if Shulk players think they lose to Incineroar (I happen to think Shulk is quite good, so it'd be pretty significant if Incineroar wins that MU).