I don't think Rikudo is in the same category as the rest of senjutsu. In the anime in order to get stronger Rikudo had to learn the same senjutsu as Naruto.
With frog/dragon you can manipulate the chakra in nature, around you.
"Rikudo sage mode" isn't the same as other "senjutsu" because you can only acquire this state if you have Hagoromo's powerful chakra or all the bijuus, meaning, almost divine power. Rikudo didn't learn any "senjutsu", it is simply when you have the 10tails' or his chakra.
It's not really fair to compare them as "RSM" basically means Rikudo vs other senjutsu, it's like Hashirama vs Juugo's senjutsu, which senjutsu is better?