Man... it's like you think this is real life or something. It's a story made up by a dude who lives in Japan. As much as some people like to think it so, this universe wasn't design to be delved into as deeply as they like. This is Kishimoto not Tolkein. Sometimes how thing appear on the surface are just that, and only anything else if the author decides to altar things to fit future plot points. Sure it's fun to theorize, but don't for a second think any one theory has much more relevance than any other if both have manga facts behind them.
Also for the last time, stop twisting my words. The first paragraph WAS necessary because you took my carefully chosen words and paraphrased to make it easier for you to debunk... or you just don't comprehend what I'm saying. Either way, I once again grow weary of having to repeat myself.
It's pretty amazing how you contradict yourself too. You say Obito can use yin-yang release w/ izunagi, yet claim he can no longer use it as jinchuriki because he didn't use it. Yet no explanation as to how or why he would have lost this ability. If I wanted to I can come up w/ several other reasons why he didn't use izunagi. Ultimately the results speak for themselves, a part of Obito wanted to break Naruto to prove he chose the correct path, and another part of him didn't really want to win at all. You also misquote Obito, he never said his Izunagi was incomplete.
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1) I didn't say we aren't privy to yin-yang release. We know it is a power only So6P had, so if there are things only he can do it's safe to assume it's due to it (i.e. Onmyoudon). We do know some things about it, but what we don't know are it's limitations. There is a difference, are you really unable to see that? Limitations like what sort of prep is needed for Creation of All Things and what its parameters are. We also don't know other uses for the release out side of making illusion into reality. I believe Kishi was showing us an offensive used for the release in Onmyoudon
2) I really don't need to explain how senjutsu counters Onmyoudon, but since you're so obtuse. yin-yang release doesn't work on senjutsu because it's comprised of more than yin and yang chakra. I hope that concept didn't fly over your head.
3) Again, yes, this a story and not even an especially deep one. It's a kids story. I'm not claiming "plot no jutsu", I gave you a reasonable and verifiable reason for why Obito didn't just obliterate everything. I feel PNJ is a term people use whenever a character acts against how they feel they should, kinda like you trying to rationalize it. I simply just except the way a character acts as part of the story for better or for worse. If you think it's illogical or stupid, well, that's a beef you'll have to take up with the author.
EDIT: You know I just realized another reason why Hiruzen's hypothesis has nothing to do w/ Onmyoudon. The attack that Hiruzen faced and Onmyoudon aren't even the same ability! If they were Hiruzen never would have returned.
Now if you wanted say Hiruzen could do the jutsu Obito was doing before he gained control of the juubi, then I agree that's possible, but would say it's still highly unlikely. Only because using combo attacks doesn't necessarily yield the same result as a blood line limit/selection using the same elements (When naruto and sasuke attacked it wasn't a scorch release jutsu). We also haven't seen more than 2 elemental jutsu combined.