I take a lot of what George has said with a grain of salt. He on one hand says that the force is not ying and yang, but on the other that is how he wrote the stories. That is what Dave Filoni has taken from it and what shows up in Clone Wars and Rebels and The Last Jedi and The Rise of Skywalker. The way I take the events of the PT is that the Jedi have slide too far to the light and have tipped the balance while the Sith have grown in power. So both sides are out of whack and in need of a reset. The Jedi think the Chosen One will come and wipe out the Sith. The Sith don’t care. So the Chosen one comes and the Sith lure him to the dark side and he helps wipe out the Jedi. Then 23 years later he wipes out his sith master and comes back to the light side. He balanced the force by resetting everything leaving Luke to rebuild. But there are still other force users out there. In The Last Jedi they made it very clear (Following in line with The Clone Wars and rebels - both which Lucas consulted on and okayed) that it very much is a ying and yang and they need to be in balance. They can be in balance in each person. Ignoring either side creates the imbalance. Luke set out to rebuild the Old Republic Jedi and was reintroducing the imbalance in the system. The force reset again, but this time finding balance in a relatively untrained person who has read the ancient texts - from the time when the Jedi were the balanced force users. So while he said no yin/yang a time or two, the end result of what he created is exactly yin/yang. He’s done that a time or two so taking him 100% as his word is not always a safe bet. I think he would have abandoned his Whills idea. Now if they were the race we saw in Clone Wars, that would have been cool, but microscopic? No.
I’ve heard audio recordings of Lucas talking to the Clone Wars writers, saying that the dark side basically is imbalance. In the recording, he says that destroying the Sith equates to balancing the Force. Obi-Wan says this in ROTS. I don’t see much evidence (outside of Rebels) that the audience is supposed to think it’s bad or unbalanced to embrace the light side. Otherwise, Luke would be “unbalanced” when he spares Vader. I’ve always felt that in that moment, he’s even more in touch with the light side than Yoda or Obi-wan, since they were telling Luke to just kill Vader.
I don’t see the force itself as good or bad. It’s dark side is not inherently bad, just susceptible to bad uses. It is the users and the orders that are good or bad. The Sith are the embodiment of evil. Destroying them will not automatically bring balance to the force, but it will end their line of evil. Balance can return when the force is used in balance. What I take Lucas saying is not that the force itself (the underlying energy of the universe) has an evil aspect, but that the Sith have been using it for evil and destroying them brings balance (post order 66) by ending their abuse of the power. Luke tapped into the dark side and didn’t fall. He’s seen that balance first hand.