"You've failed your highness, I am a Jedi like my father before me."
That is one of the most straightforward lines to be sure, but I was saying that, even if Luke was one thing at the end of the trilogy, the EU coupled with the depiction of Republic-era Jedi in the prequels strongly suggests that he went his own way after not too long. It's not applicable of course, but the Disney-SW canon seems to be moving in that direction, perhaps with a dash of Revan.

On his death bed Yoda tell Luke that he will be the last of the Jedi once he (Yoda) is gone. He doesn't say he will be the last Force Use but I never said Anakin destroyed the Dark Side, I said he destroyed the Sith - who were a major Dark-Side faction.
You were saying that the existence of Dark-Siders was in itself a cause or source of imbalance.

The conventional assumption is that Yoda chose the planet because of the Dark Side presence and that served to mask his own Force presence from the Emperor.
Still, where did that presence come from? Was it always there? Did it spontaneously manifest? If so, did it happen during Yoda's stay? Did Yoda create it through his own struggles with anger and temptation? You can make scenarios that involve past struggles in that specific location, but there isn't really a need. For all we know, there was nothing special about the cave and Yoda merely induced a transcendental experience in Luke while he was out of sight.