I would have to disagree because at one point i feel the sage had to fight the juubi because unlike madara and obit who followed his plan of sealing the juubi he did not have someone before him to mimic he had to think of sealing it himself so at one point he would have fought against the juubi as it was on a rampage because it was angry because the sages mother ate his fruit...also compared to nagato madaras use with the rinnegan is far more powerful as he was able to do as much as bring down meteors its safe. To say the sage had power surpassing even that...Many people believe that the Sage of the 6 Paths became known as a "sage" because of mastering SM. However, I oppose that.
What we know:
- Juubi see the Rikudou with a Rinnegan.
- Rinnegan is said to be the power of the Sage of the 6 paths.
- Rinnegan can help you seal the 10-tails.
- Rikudou is the ONLY PERSON in Naruto-verse that was born with chakra.
- Juubi itself = Natural energy, which the SM is composed of.
- Nagato was called the 3rd SAGE of the 6 paths, without even having the SM. Meaning Rinnegan makes you a Sage.
My explanation on my Thought:
I came under this conclusion because of the fact that Obito someone who was in a weakened state was able to become the Jinchuriki of the Juubi, no SM just a rinnegan and a sharingan.
Also, I believe we have seen the end of SM. The 3 great Sage Modes. Frog/Snake/Nature??
My theory is based on the 3 Gods of Shinobi, and how they show case the power of the Naruto-verse together and in different forms. And how 1 can do the things the other can't. Yes I am aware Rikudou is the origin of the Senju bloodline, but however the whole "genetics" thing is totally different in Naruto, evident from Hashirama having huge ass chakra and mokuton, while his parents didn't possess any.
The the 3 GOS and their unique powers:
Rikudou Sennin (non jin)-
This man has shown to symbolize the God Eye of the Rinnegan, he is literally symbolized by those eyes. And lets not forget he had powerful chakra. But notice that none of the others have the rinnegan, or became a jinchuriki of that magnitude (not saying they couldn't be, but saying they didn't). So Eye of the Shinju and powerful chakras. Also he symbolizes life and death.
Hashirama Senju -
This man, lets just start off with the name of his Clan, Senju clan of the Forest. His clan is straight up connected to the physical world. Unlike anyone before him (even Rikudou Senin) this man was born with Mokuton, the literal body of the Shinju. He also possess chakra higher or equal to the second strongest tailed beast (9-tails), He then possesses SM (another physical thing representing the BODY) that is more powerful than any other we know. And notice that none of the other 3 GOS have shown this. He represents NATURE itself.
Hiruzen Sarutobi -
This man has mastery over the 5 elements that none of the 2 have shown. He also has mastered combat forms and other jutsus. He has shown to represent what one can attain with normal chakra to the max. And the full potential of chakra without any KKGs, something Hashirama and Rikudou didn't show. He represents humans in an aspect or power of humans.
Conclusion:
Now my opinion is that, Rikudou did not have Sage mode, because he had the Rinnegan. And lets be more specific he became known as the SAGE of the 6 Paths of the Rinnegan. Not no Sage like Jiraiya...
So Rinnegan and SM enable you to get the title "Sage". You do not need SM to become known as a "sage". And Rikudou will not have the abilities possessed by Hiruzen and Hashirama. Meaning Rikudou Sennin will not show master over the 5 elements/Mokuton/SM/Combat forms. Its not going to happen.
Now this is all my opinion. Now I would like your opinion on my opinion. And please stay logical.