If you're taking the list off Serebii, then you should probably adhere to their classification system too. Other sources like Bulbapedia do not consider Ultra Beasts to be legendaries, but if you introduce a "sub legendary" category like Serebii does, then maybe you'd accept it.
The absence of paradoxes is probably because the page is outdated and not specifically because Serebii considers them beneath "sub legendary".
