You guys are basing this off the assumption we actually saw Naruto use kage bushin. He could have just as easily transformed into sage mode off screen and then use kage bushin. The fact is no one knows including the OP so really everyone needs a chill pill. Not like it even matters if he throw it in base or not.
He is high Jonin level at best. His stamina is great though. 3T Sasuke is low kage level and he still owns base Naruto so base Naruto would be below that.
When has Kishi shown Naruto to go sm off screen in these type of situations? We usually get a close up of his eyes to emphasise him going in sm.