While I agree with most of what, you are saying, something is a bit strange.
I mean, I don't really know, why people are going on about this sage mode thing, the few times we saw Minato, one can argue, that it was obvious, why he didn't use it. He would need to be standing still for a while, and it would also take a little time to summon ma and pa to fight with. However, Minato is indeed the perfect person for sage mode. He could easily escape a battle for a short time to gain senjutsu though. Anyway, this is the logical reason, but logic breaks down, when Kishi introduced his sage mode....
Because here he didn't need either ma or pa, and he didn't need to stand still very long. He was even talking and shit, and just activated it on a whim. It seems like Kishi has just thrown away all his ideals and long explanations about certain - very complicated jutsu, just to make certain characters gain new more interesting jutsu. However, one more person using sage mode, it's not that interesting :S
All in all, my conclusion is that I am kind of dissappointed with Kishi, this manga has reached its limits for what it can take. There is no more any reason to put boundary on certain elements in battle. I am expecting Minato to get nature element as well and start spitting amazing jutsu...
Hiruzen suddenly using all 5 elements...
Minato activating sage mode without standing still for enough time (and why on earth didn't he just summon ma and pa), and generally he hasn't used one summon for all this time, which is weird, the contract doesn't break, when you die, we have seen others using summons...
Also the way Kakashi has improved in skill during the war is amazing, it's unthinkable, how it's possible, and he still has chakra left after removing the arms of the gedo mazou. Even Guy is more worn out than him, though he is a super stamina freak.
Also we have seen many of the same shinobi over and over, and a few times some random fodders doing something. There are so many shinobi, that played a role in this manga, who we haven't even seen in the entire war arc, or they just had some ridicules unimportant roles. There is no reason, why Kishi couldn't have shown us them instead of random fodders dying...
So I guess what I said in the start, that it is strange, well it isn't strange at all. Past logic and unbreakable rules of this manga has already been broken countless times by the one who created them in the first place. In other words, whatever way you argue in this thread, is actually quite irrelevant. Hinata may go sage mode next chapter, nothing is saying, it cannot happen anymore

Perhaps infinite tsukuyomi have already been activated. It's the only way to explain the madness!
Or well it's quite easy to explain. Kishi wants this manga to end, and he tries to satisfy every fan. You just cannot do that without pissing others off. Anyway, I am sure his intentions are good, but it ruins the ending of an amazing story, sadly.. but money talks