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Byakugan is not a plothole. And it was never on par with the Sharingan. I doubt that it is related to the Uchiha in any way (and vice-versa for Sharingan to Hyuuga, considering that part 1 Kakashi's saying was not a developed thought and Kishi changed the story for that dramatically) and/or leads to developing the Rinnegan.
Now you saying that it's a plothole is just you being a fan. Kishi just doesn't consider Byakugan to be of big worth (at least for now) and is the Hyuugas in the series are side-characters, which is not the case for guys like the Uchiha (Sasuke being the main character), Senju or Uzumaki. Therefore, there is no need (for him) to make a side-character, which doesn't get much note, or making his jutsus, stronger.