@Damage
according to Obito he gained both chakra and ocular powers just from implanting one Rinnegan into himself. With it being so strong that he started losing himself
He doesn't say what you are implying and there is no indication he got a power boost from the eye.
Obito says
I wasn't able to implant both Rinnegan myself... Even this one eye's chakra and ocular powers are so strong I started losing myself which there is no indication he gained the chakra from the eye but opposite as he himself says that he couldn't implant both eyes at the same time because its chakra too strong and his can barely handle one Rinnegan.
Just implanting 1 Rinnegan demanding because its chakra and ocular powers are so strong Obito start losing himself which is the reason he didn't implant the other. If it gave him chakra which means more power why wouldn't he implant the other one?
Also, Sasuke's Rinnegan doesn't that demanding that Sasuke believes Kakashi can handle it and use it for undoing IT when Obito Uchiha whose half of his body made by Hashirama's cells says he can barely handle one of Madara's Rinnegan.
There seemed to be an argument at one point that Sasuke gaining the Rinnegan didn't increase his power at all. I was just trying to address that.
> Because it didn't. His powers increase because Hagoromo gave him his chakra. If you have proof of his Rinnegan incrreased his
power or chakra please share with us.
But to address the original OP's point, there seems to be not enough evidence proving that base Adult Naruto is 5-B.
> Matched Sasuke physically who has killing intent in base then tanks hit from SPS Sasuke in SPSM.
I personally don't want to touch Boruto until it concluded but: Tanked hits from Kinshiki Absorbed Momoshilki while in base who was beating Sasuke and equaled to SPSM Naruto.
Generally it seems durability feats to me. Iirc Base Naruto doesn't have an ap feat to equal other God-tiers but he gonna scale to others most likely
if Toneri did harm him with any of his non-hax attacks.
@BlackeJan
If a character's striking strength is 5-B then said character's durability is 5-B too, not the other way around.
Durability
Logically, characters capable of physically achieving a certain degree of energy output, must be able to at least withstand a comparable amount of damage, or their bodies would break apart from the strain and automatic counterforce, whenever they exert themselves.