>>50288438All the respect goes to Ho-Oh.
It was the first legendary seen in the anime. It's worshipped and revered with a wealth of legends around it, and every appearance of it is given special prominence even amongst legendaries. Other legendaries are in its service; three of which it revived and made legendary in the first place. It can only be battled on its terms, summoned with legendary artifacts of its creation, at the peak of its place of worship or at the peak of a sacred mountain range. And perhaps most importantly, It's unsullied by human antagonists in both the games and the anime. It's allowed to be both rare and powerful.
As a result, Ho-Oh is the only Legendary that feels deserving of the title. The rest might as well be oversized rats given undue attention.