Naruto: Byakugan Is the Strongest

As one of the three major pupil techniques, is Byakugan really that weak? If the Byakugan is really that weak, why is he still using the Byakugan if he is as strong as Kaguya? Doesn't she know that six magatama in the eyes and nine magatama in the forehead are stronger? If the Byakugan is really that weak and as strong as the Otsutsuki Ishiki, why is the left eye still a Byakugan? Doesn't he know that the Nine Magatama in the left eye is stronger? This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.