Yea it was a tragedy, but it was meant to happen if you think about it. (Sit tight and get some popcorn, I have alot to say lol)
In the whole Chosen One prophecy, I believe Anakin was meant to destroy not only the Sith but the Jedi as well. Balance means keeping both the Light Side and the Dark Side in check. Too much of one or the other is unacceptable and one can't exist without the other. After all, the brightest light can cast the darkest shadow... and I think we're all familiar with how that saying applies with Anakin Skywalker and his Dark-Sided alter ego...
If you think about it, no matter how much the galaxy changed, the Jedi Order never did. They were always stagnate in their hallowed traditions and rules. For all their talk of being agents of peace and constantly trying to bring balance to the Force, they never figured that their Order needed to change. Even after centuries of being brought to the brink of destruction only to be pulled back and put back on the spot of near-destruction again, you'd think they would have changed. But no, Jedi didn't change. If anything, I think the Great Jedi Purge was an eye-opener for them, to show that their ways weren't working anymore and that their Order was over. In a way, Anakin was right at the time when he was under the influence of the Dark Side in Star Wars: Clone Wars (Mortis Arc) and I quote: "From what I have seen, it is the Jedi who will stand in the way of peace."
The Sith, on the other hand, had constantly changed. Even when one of them fell, another took his/her place. They had a 1000-year plan to bring down the Jedi and rule the galaxy. And when the Empire was risen by Sidious and Vader, their plan was rewarded for a time. But even with the Dark Side ruling the galaxy, the Light Side was definitely going to come back. And it made sense that Vader was the one to bring the Light Side back, with the help of his son.
Vader and Anakin shifted the galaxy both for better and for worse, but it was all in the plan of the Chosen One. I also believe it was the will of the Force that Anakin became Darth Vader and severely crippled the Jedi Order (I believe that Anakin didn't simply choose the Dark Side - IT chose him as well). I also believe it was the will of the Force that Vader turned away from the Dark Side to save his son.
And ultimately, the balance was that the Force now had a clean slate. It had a chance to begin anew with a New Jedi Order and a new Sith Order.
This was a very cool rant! I never thought about it from that point of view... LOL. Its incredibly interesting to think that Vader was not created for just some angst but it was part of the Force's plan all along. And I loved that thing you said about the Light side also needed a check! Ha!