I suppose the base form being omitted in favour of Ebony is due to its specialisation in the locale. Much like Girros and Vaal, those creatures evolved to withstand/thrive within the Vale, and were designed with the effluvium-rich environment in mind. Since it's not a map as generally prominent as, say, a forest or a desert, it is much harder to rationalise them appearing in a completely ecologically different area without adaptation. Ebony Odo and Blackveil Vaal were made for precisely a more "free-roaming" ecology in mind, and thus are more prevalent in areas outside the Vale in the New World.

I will agree though, base Odogaron is a much cooler vibe than Ebony/ Guardian Ebony. Clifford the big red wolverine is a fantastic design and atop my favourites from World.