So let's just discard Kakashi's statement about the byakugan because we know the sharingan comes from the rinnegan.
Your 'logic' makes no sense, I prefer going by what the manga says until is proven otherwise, so if you choose to ignore that panel is up to you and your kind, not my problem.
Byakugan's relation to sharingan has not been proven wrong yet, that's my point.
You lack common sense
Kakashi doesn't know shit about the doujutsu lineage he has know acess to neither clan's secrets or history
The share fact he said "they say" proves he is not an authority on the matter
Kakashi = speculation
If the sharingan came from the byakugan it would've been clearly stated when we started getting insight about the sage & the senju & uchiha clans
If the sharingan did come from the byakugan why is said doujutsu out of the loop, period when it comes to the evolution to the rinnegan
Now tell me why the rinnegan sharingan & mokuton are the only things that can control The biju y not the byakugan
also
If u can't prove that the byakugan is decisively related don't say shit at all
Because there is absolute proof the sharingan comes from the rinnegan & nowhere is the byakugan stated to be in the cycle