Many have long pointed out the similarity of these two characters. But these similarities were limited to appearance. But now they also apply to power. And now it is hardly a coincidence.
The bottom line is that Mitsuki's Sage Mode and Toneri's Tenseigan Chakra Mode too much alike. Judge for yourself, both have a horn, both have a flame-shaped cyan chakra cloak. Hardly Kishi accidentally developed just such a design for Mitsuki.
Maybe you have any thoughts about that. It would be interesting to listen to.