I think some people are mixing up precog with the ability to see attacks coming.
Precog allows you to predict the attacks and allows you to counter accordingly.
While just seeing the attack doesnt mean predicting its next move.
That is completely true. But seeing all the different muscles begin moveing a certain way, would allow someone to predict their movements and thus their attacks.
Its sort of like how a experianced musician can actually hear what the music would sound like, by reading the musical score.
Just seeing a attack doesnt mean you are predicting it. Seeing how someone is moving their muscles and chakra etc BEFORE they attack can allow you to predict it if you are talented enough. Especially if you are familiar with the persons fighting style.
People are absolutely getting precog and seeing the attack mixed up.
Sharingan gives you both. You can actually precognitively see the attack coming.
Byakugan would only allow you to see precog if the persons attack based on their movements and how they are using their chakra.
It does not let you actually see the attack itself before it happens.
Sharingan works the same as it does vs a familiar person, as it does a stranger.
Byakugan can only work as well vs someone whom the user is familiar with.