>>40492293USUM then released, this being a year after SM's release, and Incineroar would quickly become VGC's most dominant Pokemon after getting all the right tools for being a Doubles utilitymon that does it all. Not much changed here, but it was a huge dent to owlfags as Decidueye basically got nothing that would help it in despite already being a shitmon in all formats and Primarina while getting a few new uses wasn't gifted as much either. When compared to Incineroar, there was a clear bias and this is when things started to run out.
There's a lot more to this story, but the final and most damning thing was obviously Smash. Decidueye was a shoe-in! We needed a Grass type rep! Ash was getting it! It was already chosen for Pokken! NEXT GRENINJA! And then, whoops, Incineroar was confirmed which fucked not only all the owlfags but the grinchfags, too. If it wasn't already, this is when Incineroar became the shitposting mascot for good. It wasn't about design, popularity or even what it got. Incineroar represents "BTFO culture" in its greatest form. BTFO denialfags, BTFO owlfags, BTFO animefags, BTFO compfags, BTFO smashfags - you name it. Three whole years of silly wars culminating to this point. Probably the most popular of the final stage Alola starters by now thanks to Smash, but honestly the three are pretty equal with each having their own crowds. It has its genuine fans for sure and I feel sorry for them but a lot of what you'll see regarding Incineroar, at least on this site, is as you said a lot of shitposting and some people to their own admission only like it because of how other people view it.
In the end, however, it was all TPCi's fault for shilling Greninja so hard and putting the idea of "next Greninja" into people's heads. Greninja (and Charizard) shilling singlehandedly ruined two whole generations of starters and I won't even be shocked if it happens a third time with this generation.