I think I have an idea as to why XYfags in particular hated SM the most, while OS/AG/DP/BWfag hate of SM was much less vocal. I think it's because XYfags were so sure that XY would be the series where Ash would finally win, only to see Ash get BTFO so hard. In addition, XY was the final series to have the traditional Pokemon anime format and artstyle, with SM and now PM2019 being more experimental in terms of design and writing. Notice how XYfags hated SM from the start due to how different it looked and felt. They probably felt "betrayed" that this "different" series being the one where Ash finally won. Meanwhile, fags of older series had seen him lose so many times that they got desensitized to it and stopped caring if he won or lost. Meaning, when Ash won in SM, it was easier for them to feel "at least he won for once" instead of "why couldn't he have won before?"
