As both a Chiefs fan (KC native) and secondary Bills fan (weird, I know, but it's complicated) I think the fanbases are mirror images of each other. Both are loud and passionate. Blue collar, for the most part. Small market. A history of heartbreak.
I've never met a Chiefs fan that didn't admire Josh Allen and respect the Bills organization. Of all the Chiefs' rivals, the Bills are the least "hated" from what I've seen.
Can you point me to specific examples of jerk KC fans? Of course! But you wouldn't have to look too hard at every fanbase to find the same.
I can only speak for myself, but during this magical run I've heard Chiefs fans praise the Bills more than any other rival. Or at least give the grudging respect the Bills deserve.
You should hear Chiefs fans talk about the Raiders, Donkeys and Bolts -- screw those teams and their fans!