It isn' t a need, it' s an observation and the whole manga is made around the fact that genetic matters.
It is a valid observation, not more than a speculation.
But people are forgetting that Sakura is supposed to be the epitome of the average person, someone who came form a humble family and became a kunoichi of her own ability. Associating her with the Senju clan is a rather big betrayal to her character, that is all I'm saying. Senju or not, Sakura found her own end and that counts as something independent of her genetics.
Sometimes it is ironic how people themselves ruin Sakura for everything, in general.