Okay people, let's try our best not to turn this into another XY vs SM fan war okay? Don't use this thread as a free for all buffet for bashing XY and the same goes with SM. I mean I hope that's what every user does except for those whose names rhyme with Bane and Brisket
Anyway, into the topic of this thread
XYZ, despite your opinion on it, certainly had a MAJOR effect on the fans and writers and had rippling effects. It certainly was controversial in the end, a huge majority HATED Ash losing in the Kalos League and many were displeased by Greninja being released. However it's also true that a majority loved Serena kissing Ash and the Team Flare arc, atleast during those moments, until after more criticism towards it came into the picture, specifically Serena's dialogues during the elevator scene
I do think the Kalos league backlash was a pretty significant thing that the writers took note of. Heck if I'm not wrong the preview for next episode got review bombed so hard they turned off likes and dislikes.
While Ash's alola league win happening was more due to the structure of the region itself and the game story, there is no denying that the Kalos league backlash also probably influenced the decision as well as the decision to respect Ash's strength as a trainer and allow him major milestones, which is why we follow up with JN's PWC rather than the Galar league
Now as to the fans perspective of it, XYZ deserves MAJOR CREDIT for having a hugely invested fanbase at the time it was airing, regardless of your opinions on it you cannot deny the hype was at an all time high during the days of XYZ, while I believe the major credit goes to the artstyle and stellar battle animation, you had old and casuals alike invested. With the marketing taking advantage of the hype and baiting them, it was no surprise the backlash would be huge when things didn't go their way. XY despite its ambitions never quite felt confident enough to take the journey to the position it needed to, even if it broke anime's molds and structures. To then be unsatisfied with how it ended AND seeing the SM's change in tone and style, toxicity ensued, seeping into when SM aired and it getting massive hatred simply for not being XY, something that sadly some people still do rather than look at it for what it is on its own
Now for the writers perspective on it, I believe XYZ and the whole process of it, the production and the reception, is what finally convinced them to break the mold, the old structure. I'd say it has more to do with how taxing it was to have a show with the level of XY's production, especially with the 3D camera. I also imagine the writers felt extremely tired of the old lethargic formula and repeating it again next series would be suicide because no one would care anymore, they needed to reinvent to make people believe again this anime will ever go forward with Ash again. One of the major reasons for the backlash against the Kalos league was the fear of Ash's stagnancy, especially when they assumed next series is a reset again and Ash is a rookie again
When it comes to JN, no the "crew hates XY" conspiracy theorists are dumbasses. But i do feel the writers of JN were very careful when it came to XY, for them it was no doubt a special series they had to carefully maneuver around, esp BECAUSE the style of Ash in SM and JN doesn't really match with the style of Ash in XY. And that is why I think amourshipping (which still had significant hints mind you) was kept to a minimum and not followed up on, as well as Ash-Greninja, because that is something for the XYZ characterisation of Ash specifically and it's design rather than JN's take. So they didn't want to piss on the old series or change their direction, so they decided to sidestep it. Why not atleast include AG in the XYZ flashbacks? Beats me, it was a dumb decision not to but I doubt arises from them wanting to retcon it happening. Same with Alain probably, they wanted to use him because he's a popular character the writers also like and thought would be a cool 8th member wildcard but was so massively underused because they wanted to sidestep around the whole Ash-Greninja stuff, which was a Crux of Ash and Alains relationship and not wanting to explore that means Alain doesn't really get significant time
All in all, I do believe XY's popularity and "fanbase" will always be at odds with the direction the show went as a result of XY. For better or worse. But I do believe after JN it doesn't really need to be a sore point unless they make Ash end up with a different girl or ever do something similar to JN again, of course for the fanbase, they'll never stop screaming for more that they wished XY delivered