This is all subjective and you haven't proven me why Hebi Sasuke would be Sannin Level simply based on being Tsunade's superior. What you're telling me is that Hebi Sasuke is more equipped to handling more opponents than Tsunade is which is not only unsubstantiated, but gives the impression that Tsunade lacks versatility and isn't even worth considering for the Sannin Level position in the first place. There's absolutely no logic in you perceiving Tsunade as Sannin Level yet lose to majority of characters that aren't depicted as Sannin Level.
I'm not going to conform to your line of thinking unless its actually necessary because all of these opinions on how well Tsunade can operate against most opponents is according to our own subjectivity and isn't set-in-stone.
I say Sasuke beats Tsunade = matchup excuse
I say Sasuke pushed Itachi = matchup excuse
I ask you to list out characters Sasuke and Tsunade can beat = "don't want to because I know I'll prove your point"
How does this pass as an argument? Literally anything Hebi Sasuke does would be a matchup excuse, Its funny if I bring up Deidara who low diffs Tsunade you'll bring a matchup excuse again, and then to validate Deidara in a tier ranking the person Deidara beat (Gaara) who low diffs Tsunade would be a matcup excuse too.
When almost every other character is a "bad matchup" its not a bad matchup anymore, it means something is clearly wrong with the character you're defending
Also there is more to being a ninja than combat skills, Tsunade is exceptional in the medical field which is extremely useful in battle, that alone puts her at Kage level.
