He's >= The Last Sasuke >= Teen Sasuke
I think he means durability since he's hung up on The Last Sasuke being unknown(
I fix soon) And because he's weakened in the Shin fight.
Various statements of being relative/an equal to Naruto(who has been 5-B since Shippuden and far stronger now) from the Manga, databooks, light novels, etc. Along with feats that back this up 6 months later in the Momo Arc with no implied strength increases from Naruto or Sasuke since then.
His being weakened isn't a good enough argument either.
Sasuke shows no signs of fatigue or exhaustion that would suggest a drop-off in power big enough to warrant an unknown rating.
Hell, Naruto couldn't even tell he was weakened until Sasuke brought it up.
Not to mention the reason he was low on chakra, to begin with, was that he had to teleport to Kaguya's palace and at the very beginning of the Momo Arc we see that he teleported to Kaguya's palace and still stalemates Kinshiki(also 5-B)
Your best shot at changing some minds is being able to prove that Shin Arc Sasuke is far inferior to Momo Arc Sasuke(statements or anti-feats might help.)
Shin himself wouldn't be an Anti-feat since his fight with Naruto and Sasuke sets the precedence for his scaling.
Saying "That Sasuke is from a future arc so he shouldn't scale to a past Sasuke" is just a bad argument since we do accept back scaling if it's consistent and you have no supporting evidence to back up your opinion.
It also blatantly contradicts the Narrative of the Momo Arc with Sasuke's equal, Naruto, being negligent in all aspects of his life due to his Hokage duties. Yet they are shown to be just as relative as they were stated to be in those examples I provided. (some of which were before the Shin Arc.)
If you don't have anything that further backs up that opinion of yours we're basically done here.
Not that that's for me to decide you can try and look for more staff and see if anyone shares your opinion.