Now imma just elaborate on something, I think Incineroar could very well not be real and insiders are wrong for whatever reason on this.
I just don't think leak bait is likely lol.
I think
DaybreakHorizon
gave an excellent reason for the leak bait argument being faulty. Why would Nintendo use a character for leak bait and then tell everyone--unless they're all getting it from the same source, which if they did I would highly question their journalistic practices, then it defeats the purpose of a leak bait, which is to catch specific sources of leaks.
That being said, I feel like the insiders could be right along with the image, so long as Incineroar isn't shown off before the other characters (a very convenient kill switch). Unless they give a more conclusive reason (e.g., a character is in the banner but not in the game), I'd rather not take their word fully on authority, as they may be using faulty assumptions. There's also the chance it was a cut character, or moved to DLC, and they have outdated information, but I consider that less likely, given their conviction.
All that having been said, as much as I think they did a disservice of escalating the situation by addressing the aggressive fans by being aggressive back (to everyone who believed in the leak, aggressive or not), I do take their consensus seriously, and is the last major hurdle against the banner, for right now. Just the convergence of evidence surrounding the image and its circumstances outweighs that consensus, as of right now, for me.