4-C Naruto & Isshiki
Kaguya's attack has 4-C Ap. Kurama says about Isshiki, "He is a completely different monster than the ones we have fought so far." According to Kurama, Isshiki is the
strongest opponent that Naruto and Kurama have ever fought. It is also stated in the episode description that Isshiki is the strongest enemy. ''These two statements only apply to Isshiki Ap>Kaguya Ap. You may say "ETSB, which is 4-C, does not cover Kaguya". However, ETSB Kaguya is also technically an enemy, and Kurama has seen her strength as well.
4-C Momoshiki, Kinshiki, Gokage
Sasuke has knowledge of how powerful a character can be with his Sharingan. Although ETSB has seen Kaguya, they think Momoshiki and Kinshiki may be stronger than Kaguya. Then he says my hypothesis was correct. There will definitely be people who will not accept this. So let me give the following examples: When Sasuke, who has Sharingan and Rinnegan, sees Kaguya, he realizes that Kaguya's chakra is
better than Madara's chakra. As soon as Pain, a Rinnegan user, saw Sage Mode Jiraiya, he implied that he had
powers similar to Orochimaru. Tobi
states that Sage Mode Jiraiya is a power worthy of the Sannin level. He had already seen Orochimaru before. While Madara fights with Sharingan against other shinobi, KCM switches to Rinnegan to react to Naruto. These come to my mind for now. There are many characters in the series who can feel their opponent's power by looking at them.
Not only with eye power, sensor type ninjas can sense how strong their opponent is. Naruto realized by feeling that Edo Nagato was stronger than the Pain he fought.