I think Korra is in a way supposed to emulate Wan... a little bit. I mean... he had his imperfections. I mean, of course he wasn't as bad as many others (he did share, he was maybe a little arrogant) but the general view is that humans... weren't viewed as ideal. Even those well intentioned (Wan's friends) didn't necessarily... get it right.
And I think this is getting a little bit back to Korra. She... should be getting better after this, I think. I think this was the grand realization point for her. In a way. I think she's supposed to come about after this.
As for the bending.... I think that there is a difference between gaining the power and learning to use it well. I noticed that when they requested an element, they said "Please grant me the element of...". They never requested a bending ability. Just raw power. And then of course we saw that there was a difference between their power usage (raw and untamed) verses Wan's (refined and informed), because Wan had learned from the spirits which knew it as well. My guess is as time went by, element-holders learned how to refine their abilities, and this became "bending".
Sort of an analogy... if I give you a car, you have a car, and you can hit the gas pedal and such, but you're likely going to hit a tree. You have the ability to operate a car... but not really to drive. But by finding an accomplished driver... you can learn from them how to truly drive. It's the difference between gliding along smoothly and spiraling into a tree.
If that fails to explain... well... Imagine how many things we've twisted up over the last 10,000 years.
Anyways... the Wan story was awesome. Wouldn't mind going deeper, but we should return to Korra's story. I have a feeling it's going to be great. But Wan later.