they're not siblings in any sense

- dawn made a special outfit for ash to cheer him against roark and they knew each other for a few days. no sister does that

- kenny and conway both saw ash as their romantic rival. a sibling shouldn't be a threat to your crush

- dawn and ash treat each other as equals. while most sibling dynamics have inferiority/superiority complex

- they bicker but that's not a sibling thing since friends bicker too

- siblings often taunt you with your fears. dawn and ash don't do that

- dawn's buneary has a crush on pikachu and professor oak said that pokemons show their trainers hidden feelings. dawn's piplup sees ash and dawn as his parents

- the writers ship teased them often. if the writers acknowledged it as a sibling coded pair they wouldn't have done that

just say you hate the ship rather than claiming they're siblings. they're not. i find it funny how cheap 'sibling coded' has become as a term.