learning SM made chuunin level naruto a KAGE level shinobi,in a sense that he could compete with pein.
Now lets explore BM Naruto's recent abilities;-
1.he owned 5 bijuus.
(2.held his own against madara and even protected kakashi and gai once a while.
3.tanked a juubi laser tbb with minimal difficulty.
4.held his own against juubi,even though he was clearly outmatched.
and others i might ave forgotten.BM placed naruto as 4th strongest.
Now since SM exponatially increases your abilities,how do you think BSM is gonna be if it was showcased in battle.
i just want to clearify the OPness of BSM.
since people claim it does nothing but make naruto's attack effective against juubito,which is wrong.
I agree overall but you're mistake in what you first said. Naruto base was jounin level upon learning SM. Kakashi stated that Naruto was on even standings with him or even surpassed him when Naruto learned rasenshuriken, he said it after Naruto beat Kakuza while they were in the Ramen place. Naruto's base has gotten even stronger after learning SM and even handle Bee's 2 friends with ease when they went to Konoha for info on Sasuke, Naruto only got pushed back because be was protecting Sakura.
Pain's fight was handicapped, Pain used Almighty push which weakened him and Naruto was training before fighting Pain and used 2 clones which makes his power 1/3rd on the field.
Naruto has the fire power but still new to them so after mastering his powers and training for a few years then he will be 1st no doubt. Great thing about Naruto's training is that he can use shadow clones to increase is training time over 100x. He used 200 clones while learning wind elements which was 200 days of training in 1 day, he trained for a few weeks to a month in total. He was being cautious of his clones losing control and going cloak mode but since he has Kurama, ne can use even more clones to better his training even more but since we know of 200 clones I'll use that. So if Naruto trains for 3 years with 200 clones, that's 200 days worth of training per day so that's like 219k days of training in 3 years.
He has to potential to be stronger than anyone really.