The first successful blood-transfusion was performed in 1667. Given that the time of the Sage may very well have been MORE technologically advanced than the "present" of the Narutoverse (without ninjutsu, how the HELL would people survive free-roaming apocalypse-beasts without technology?) I see no reason why they shouldn't have the know-how. I can't see the Juubi acting up enough to get sealed as BENEFICIAL for the global technological level...
Correction: 1818 was the
first blood transfusion that you can use to make any argument with.
All documented instances before that point in time involved the transfusion of
animal blood.
Everything you bring up about technology
is speculative at best, don't argue with it.
The Jubi is known as the progenitor of everything that exists in the world, essentially a god.
Not to mention, even if your highly speculative ideas did come to fruition, why did the Sage have to seal it?
The Sage was a shitty father. Competition between siblings is natural, even healthy. Active hatred of a sort that leads to generations-long feuds is something quite different. When the Firstborn Son got snubbed, presumably he expected his father wouldn't DISOWN him on his DEATHBED for following a philosophy very nearly in tune with the Sage's own... He didn't take it well. As any reasonable human being would know.
It's not a matter of how good a father he was... The younger son
wouldn't give blood to his sworn enemy.
The older brother would have to do the same thing as Madara, take DNA by force.
With that being said, we know they were always at stalemate.
I don't believe the Sage desired power as a path to peace, but he sure as hell ended up with a ridiculous levels of it. And if ANYONE in the world had power to create lasting change, it would be obvious to the Firstborn, and indeed anyone else, that it would be the Sage.
Until they die... for as strong as the Sage was, he ultimately died. Warfare resumed.
How is this "testing the limits of power"? I woulda thought REDUCING the amount of power any being has available (like he did with the Juubi) is just leveling the playing-field a bit between demons and humans?
Indeed? Well then why couldn't the Sage have taught it to people?
I'm talking about the Sage
telling his sons to do anything like blood transfusions. He wanted peace.
Your question is just awful, you've already stated that Uchiha + Senju = Sage
He can't just teach people how to do Creation of All Things. As to why the sons can't, I've explained.