He was taught the technique by a Shaman, therefore he did learn the technique. Much knowledge of said techniques was lost in the former wars against Dark Jedi, even as far back as the Jedi Civil War.
You've misunderstood me, so I'll clarify: he wasn't given instruction on this technique from another Jedi -- something that isn't common knowledge anymore. That the most powerful Jedi in the history of the Order (a Jedi over eight centuries old) was ignorant of the technique whereas Qui-Gon -- primarily due to his lack of blind faith in the Force and in the Jedi Order itself (he was realistic, not stupid) -- learned it. Yoda himself says that he still has much to learn, which is why he dedicates himself to becoming the late Qui-Gon's "apprentice".
The Jedi and Sith have "grown stronger" based on quotes?
You had to ask, lol, at a bad time. You'll have to wait before I can provide the quotes to you verbatim, as I don't have my copy of Labyrinth of Evil on hand. However, the omniscient narrator reflects that "two-hundred years before the rise of Darth Sidious, the dark side had been gaining strength" -- and "the Sith, too, were pleased that the Jedi had been allowed to grow so strong" (it goes on to mention, I think, that it would make their 'victory' so much more sweeter).
I've already stated my distaste in such measurements of power and skill.
That's true, but it doesn't make them any less valid, especially when the quotes are dictated by the omniscient narrator. George Lucas (the guy nothing -- not even feats and accomplishments can contradict) himself has referred to the prequel trilogy as "the prime of the Jedi" and "the golden age of the Jedi" -- and since the greatest war (up to that point) was coming into fruitation at that point, I highly doubt he was referring to 'peace' (and statements have been made that the Jedi 'dwindled down' to a 'mere 10,000', thus removing the possibility of referring to numbers).
I believe that feats and accomplishments show much more, and judging from the average Jedi and both their terrible abilities at the Battle of Geonosis and their terrible performance against Dark Siders in saber-to-saber combat, I disagree that they're stronger at all.
I'm sorry you feel that way, Se7in. But the fact of the matter remains. The Jedi were fewer in number and -- according to several sources (Yoda himself included: "blinded are we, if forsee the development of the clone army, we could not"😉 -- the Jedi were losing their ability to sense the future with the Force. It's not a stretch to assume that this would also include precognition even in battle. Nevermind the simple fact that their adversaries possessed technology and capabilities that vastly outstrip anything prior. The CIS or Republic would utterly curbstomp the **** out of any faction present in the Great Sith War, so why is it so difficult to believe that they simply weren't winning?
Meanwhile, what terrible performance against dark siders? You mean the dark siders who were certainly weren't being hindered by the rising dark side?
Why is it ridiculous to compare the two? A war against armies of Sith has less stifling effects than those against a hidden enemy? Granted it is mentioned, that to me makes no sense.
It's not so cut-and-dry, Se7in. Those 'armies of Sith' aren't coming close approaching the level of strength in the dark side possessed by Palpatine (who is a "black hole of the Force", "an event horizon", "darkness beyond darkness" according to the RotS novelization) and his apprentices. The fact that the Chosen One was destined to act during this time ought to make it clear that the Force was in a great tumult (specifically, it was unbalanced) whereas that was never the case during the Great Sith War.
"... And in the time of greatest
despair there shall come a savior,
and he shall be known as:
THE SON OF THE SUNS."
Journal of the Whills, 3:127
But the price of comfort was weakness. The institutions of government became decadent and Jedi numbers dwindled to a mere ten thousand. Now, the Force itself is unbalanced and great change seems imminent.-- The Complete Visual Dictionary, page 12.
I can find more. But to compare the two is ridiculous, as I said. The PT Sith caused far, far more damage and destruction and unbalance in the Force than any Sith prior to them, ever.