It would be better for you to see the movie before you start judging it's contents rather than seeing a few clips and then thinking you know what's going on.
I. It's stress, Naruto creates countless amount of clones to do side jobs throughout the village, not three or four. If I would put an estimate ... I would say at least hundred.
No, the problem isn't Naruto's ability to use the shadow clones, it's how they operate. He uses shadow clones but they usually work for a limited amount of time. For example you wouldn't see Naruto use shadow clones in a battle all day, but this Naruto has clones that work for him contentiously all day long. Add that with the physical strain it puts on him afterwards, he's basically in an overrun continuous lap of overworking himself.
I've never heard such a statement where Naruto/Kurama molded chakra together and that was a sign of rust. They did that in the War Arc together, and they did it with Minato/Yin Kurama. So I don't know what kind of crap that is either :lol
Yeah Naruto was waiting to be saved, but he wasn't the only one that 'needed' to be saved in the fight. lol
I don't know what "rust" your referring to, both Naruto/Sasuke made a few mistakes but it wasn't oriented. Naruto fell on some rocks (I'd have to look back for the reason) but it's the same excuse you have when Sasuke was captured in chains and then slammed to the floor, and then he was later blasted with a fire release type technique and his face began to burn off.
Overall Naruto/Sasuke weren't "rusty", it's just that Momoshiki was that great in battle, despite the 'nerfs' on them only using Taijutsu/Kenjutsu.
Since Naruto's chakra was absorbed in the beginning of the fight, it all caught up to his body towards the end and his chakra mode went off. Sasuke couldn't come to his aid either, sadly.