It's not plot no jutsu or etc. He already explained either. First of all, he wasn't true wielder + don't have monsterly chakra pool like Nagato. While He's always using his MS. When He became Juubi Jin. He can't even use MS due to control juubi, already unstable even in So6P mode or whatever you call it. Well yeah he can use some shinra tensei for surprise attack maybe but at this rate, Naruto already able to reflect few TBB. If Obito wants to throw Naruto so badly, He needs to use really good amount of chakra which would be just wasted. And still There's a option like he couldn't manage to control all paths or able to use since he just wield them short-time and he wasn't the true wielder. Sorry to say but Minato's SM was more forced than this. There are few explanations or options for Why Obito didn't use any formal 6 paths