The manga was always loose with the word "senjutsu". It was used to refer to the actual chakra, sage mode itself, and the techniques at different points in the story.
So it really ain't shit to argue about. Sage Mode training isn't required to handle senjutsu because "senjutsu" can mean several different things if we're going by the manga. If we're talking about Juugo, a guy born with the ability to convert nature energy, no training required. If we're talking about Madara or Sasuke, two guys who needed to be given the cells of people affluent with handling nature energy to access the chakra, no training required.
Hell even Naruto technically didn't "need" the training at first. He only went through with it because Ma and Pa couldn't attach to him and give him a shortcut to senjutsu like everyone else. "Senjutsu", the Rinnegan, Hashi's cells, all the same shit. Just another power-up that everybody wanted and took mad shortcuts to get.