To Travel, you need to know your point of departure in any case, not your destination.

Does it really change something? You open the Gateway and the location is not the same. You still end up somewhere that is not where you wanted to go. Ocean instead of a city, mountain instead of a forest. In the end, Traveling became unusable because of the changes in the landscape.

Your point about other planets is also, in my opinion flawed. Whose to say they used Traveling to go there and not some other means lost to us now. Even so, even if the planet is moving in space, the physical location on it's surface is the same and maybe that's all the Channeler needs to Travel.

And also because RJ needed that the main protagonists be more "special" and find out those weaves and use them almost exclusively to their inner circle, at least in the beginning.

I also share your thoughts on the easiness everybody has to copy weave and I like your analogy on the symphony. I guess that this late in the plot, the story doesn't center as much on the complexity of weaves and learning to use the Power, but more on the conclusion. See how cleansing the Source was done and how fast (in pages) it happened. When compared to the time spent showing us the girls in Tar Valon learning OP related stuff, it was done really fast. RJ even had to explain it to some readers on his blog. He focused more on the symbolism of the Cleansing than the way it was done.