Were Senju necessary, Kishimoto?
With the last chapter ( for future information, 606 ) we've got the confirmation that Uzumaki = Senju in inheritance, meaning that, bluntly, Senju are relegated even more in the trash can as they already were ( I mean, you have a bunch of Sharingan-wielding Uchihas and you only have 1 Mokuton user? ).
Senju's worth was, up until now, basically having the Younger Son's body and pure inheritance, while Uzumaki were basically "distant cousins", very much like one can assume Hyuugas are for Uchihas.
With this last piece of information though, I can't help but feel how useless Senju are portrayed by the author, almost like they were just stuffed there to make a connection that wasn't with Naruto, for reasons unknown ( since Naruto and Sasuke are compared to Hashirama and Madara since part 1 ).
Objectively, Uzumakis have received the gifts Rikudou bestowed upon his Younger Son, while Senju don't have shit.
Let's compare the two:
-Bigger than average chakra reserves
This basically makes them equals to non-Sharingan Uchihas ( remember Sasuke? Above average chakra reserves and outstanding talent ), which makes them good, great ninjas, but nothing more.
Hardly someone discending from Rikudou Sennin.
Now let's take a look at Uzumakis:
-Bigger than average chakra reserves ( Naruto, Nagato, Kushina, Mito )
-Special kind of chakra ( Karin, Naruto, Kushina, Mito )
-Body capable of withstanding and housing tailed beasts ( Naruto, Kushina, Mito )
Uzumakis have basically the body of the Sage:
great chakra pools, incredibly resilient and with great longevity, and also capable of housing tailed beasts, just like Rikudou did in the past with Juubi.
If we want to compare the two lineages, a fully matured Uchiha can, by all means and purposes, be equal to a fully matured Uzumaki, while a fully matured Senju wouldn't have a thing on either of these two.
This is even more true if we take into consideration special powers:
Uzumakis make perfect Jinchuurikis while Uchihas can awaken their Mangekyo, while Senju are left with nothing.
basically Kishi could've given Senju all of Uzumaki's redeeming features without the sealing jutsus, and made Naruto just a "normal" kid.
Or, if he wanted to link Naruto to Rikudou by force, just make Uzumakis the originary clan and let Senju be known for what they theorically are, the Younger Son descendants.
This is under the premise that I did not include Hashirama as a standard Senju, since his powers were never found in other Senju and he is, thus, an anomaly, while Uzumakis powers can be traced in all Uzumakis introduced