There is one think I do not like about power building in Naruto series, and though I don't complain often about it, it is worth mentioning.
Kishi always build unreasonably a powerful character, then end up trolling it with a trollish weakness. KAbuto paid the price (Izanami) and Obito is paying his (SM). Who is next?
A. Now, let look at some facts:
(1) In Naruto vs Nagato, and later edo Madara, we have seen that Rinnegan can absorb all ninjutsus. In fact, Nagato's path absorb many of Naruto's sage Jutsu.
(2) When Juubi appeared, it was said that Juubi is a mass of natural energy. While I don't think that this means that Juubi is unable to create chakra, many people considers Juubi has pure natural energy.
(3a) Obito has Rinnegan, and unlike me, many people believe he can use all the paths.
(3b) Many people believe that six path techniques are the Jutsus solely available to people who have Rinnegan.
B. Fact analysis
From (3a) and (3b), I think that it is logical to think that Obito can use all six path techniques. Fact (1) strongly suggests that Obito can absorb chakra of any nature including nature energy base chakra (aka SM Jutsus). Given that the Juubi inside Obito is a mass of natural energy, fact (2) tell me that Obito should be able to absorb SM Jutsus without any consequence. In fact, we can ask why absorbing more natural energy would be detrimental to someone who has fuse with a mass of Natural energy?
Clearly, while I don't know the reason behind Obito's vulnerability to SM Jutsus, there is no good reason to explain why he cannot use chakra absorption Jutsu to absorb the SM Jutsu. There is no reason to explain why he cannot perform wide scale Shinra tense against Naruto and Sasuke, etc.
Of course, in my conclusion, I am assuming that Obito can use all Rinnegan Jutsus. However, can he really all the rrinnegan Jutsu? If he cannot, why is he not able to use all Rinnegan Jutsu?
To try to answer these, let look at Madara, Obito, Edo Madara, and Nagato.
C. On Rinnegan users
Madara unlocked Rinnegan, said he was old and almost dead, then gave his Rinnegan to Nagato in order to revive him. What if actually, Madara gave his Rinnegan away because he could not handle it. What if it was because his body did not meet the requirements to use Rinnegan that he had to give it away. One confirming supporting argument is what Kabuto said. Kabuto said that he deciphered Madara's body. Thus, he and Orochimaru made a new hypothesis that was beyond what others did - referring to Danzou.
Interestingly, what Danzou did was to replace only part of his body with Hashirama. It also seemed that Madara did the same - that is he only place a piece of Hashi to close his wound. Thus he needed life support. Concerning this, I have hypothesized that Madara got too old because his body could not handle Rinnegan after he unlocked it. This can be seen with Kakashi just after unlocking MS. Kakashi had to mature before he can re-unlock and use the MS - actually 14 years or 16 years after he unlocked it.
Obito has the worst used of Rinnegan. In fact, given how Naruto is talking through his chakra to others now, if we assume that anyone can control dead bodies though chakra connection, then we can conclude that Obito has never used Rinnegan. The reason is that the only things he did was to control dead bodies, and actually, he had been controlling Gedo Mazou similarly as well, except Gedo Mazou had 9 eyes.
Interestingly, it turn out that Obito also has a poor body - that is partial Hashirama's cell+Madara's on one side, and plain Obito on the other side.
He has a perfect vessel made of Hashirama's cell. Thus typically, his eco was young unlike his older body who died in the cave. This has made debate on this forum before. Interestingly, Edo Madara has been using Rinnegan consistently with a meteor pulling from the sky.
Note that the difference between Madara, Obito, and Edo Madara is that the later has a perfect body, or a Senju body. We even saw that when eco Madara was summoned, he did not have Rinnegan, and he was not surprised. However, when he unlocked the Rinnegan, he got surprised. This show that Edo Madara was not expecting to unlock the rinnegan because it is not a power that belong to his original self. Rather, it can be obtained only by some science.
Now, notice that unlike the real Madara who unlocked Rinnegan when he was almost dead, Edo Madara unlocked it instantly. This again suggests that the full Rikudo body is necessary to unlock Rinnegan. Madara's use of the Rinnegan also show that the full body hypothesized by Kabuto and Oro is playing its role unlike Obito and the true Madara when he was alive.
He is the best Rinnegan user of the manga. He only got the eyes implanted, and had a body that is Uzumaki. Now, I am certain I am not the only one who believe that Uzumaki have feat that is even closer to Rikudo's body legend than the Senju (except Hashi). In terms of statistical distribution over the people shown, it appears that Uzumaki are more special than Senjus - body feats-wise.
Thus, I can hypothesize that Nagato was able to use Rinnegan because he had also the full body of Rikudo.
D. Some Hypothesis
Going from Obito's poor use of Rinnegan (or maybe no use at all), old Madara giving his Rinnegan away to an Uzumaki rather than a young naive Uchiha (which he could find), Edo Madara instant Rinnegan unlock and being surprised because his body was deciphered, and Nagato, I think these hypotheses below can be true:
H1. To use the Rinnegan, you need a specific Body, which Rikudo had. The only clan that has this body naturally is Uzumaki. This body can be obtained by a perfect fusion of Senju and Uchiha body. Partial implant of Senju body in Uchiha cannot give that body, and therefore delay Rinnegan to when close to death.
H2. Even having Juubi's power, Rinnegan, Senju Uchiha half body, Obito was still unable to do six paths. It may be also possible that six paths techniques are available only to those who have the full body explained in H1. This at least could imply that Rinnegan is not the sole source of Six paths technique.
I am sorry for the length. I hope you enjoy it.