Yes, you're right. Momoshiki's ability is too OP. No wonder Kaguya needed an army of Zetsus to fight him. For example, Kaguya's chakra punches destroyed Sasuke's PS. But if she uses those chakra punches against Momshiki, he'll absorb them and use a 4x stronger version against Kaguya. GG.
Kaguya cannot use any ninjutsu against Momoshiki because he'll absorb them and wreck with a much powerful version. She can't use genjutsu because Rinnegan nullifies all genjutsu. She can use taijutsu and she's much weaker in taijutsu compared to Momoshiki+Kinshiki. Teen RSM Naruto was overpowering Kaguya in taijutsu, and Adult Naruto who was more powerful than Teen RSM Naruto needed another same powered partner (Adult Sasuke) just to match Momoshiki+Kinshiki's physical parameters and taijutsu.
He most probably can absorb Susanoo and TSB. And that'd definitely be the end of the world...