It's kinda sad, but mostly just fucking hilarious to witness our resident sake brewers tying themselves in knots fighting against the manga canon. It's so easy for them to get triggered cause all you need to do is post panels and facts from the actual manga, and it instantly shatters their entire fanfic reality.
They hate that Yamao has such a close bond with Momo. Absolutely despise it. Cuz they fully recognise the damage it does to their headcanons (even if they won't say it out loud.)
^^ This is her most character defining moment in the manga. A character utterly delusional in her roleplaying. Yet here she is, proudly proclaiming who she is,
by her real name. Aaaaaand...this moment occurred in the context of her declaring her immeasurable honour and duty to Momo.
They despise this. As well as the fact that her devil fruit is literally known as "The Guardian of Wano". The truth is so blatant yet so resented that merely pointing it out has these people seething. They'd muuuch rather it never existed to begin with.
Same goes for the nickname Yamao, that's met with such disdain. Some literally act like it's tantamount to the n word. But really, they don't actually hate the name. Rather they hate the fact that every single time it's used, it reminds them that the MC couldn't give less shits to remember what their favourite character is called.
The Yamao they love and enjoy, exists solely in their fantasies. In reality, they despise the character and her role in the story with Momo, which is why they subconsciously rewrite it in their heads.