No you asked why they could become Sulong before, because Oda conveniently left a hole for them to see the moon through, Oda can conveniently then use Kaido's abilities to obscure the moon.
Neko/Inu are not main characters, them having the stakes upped and influenced by Luffy/Kaido's battle adds to the scene and doesn't take away anything.
In a fair 1v1 with Sulong they would win, but due to Kaido's interference they lost Sulong (not their fault), similarly due to Luffy's interference Kaido's interference was negated...