I seem to remember the original plan for the series was a trilogy, where book 1 was supposed to be everything up to the ending of The Dragon Reborn. But Jordan was a bit of a discovery writer and everything became longer than planned. And then even longer, and so on. 🙂

I love seeing people mention books 9 and 10 being among their favourites. It indeed is a personal thing, and writers should approach every scene like trying to make it so that it will become someone's favourite scene in the book. Every reader is different, everyone has different preferences, expectations, interests, backgrounds and so on. As long as every scene and every book has something special, something to recommend itself, you're doing okay as a writer. Not everyone will like it, but that will be the case anyway.

I think this is where we should look for the answer, but it's hard to say. Jordan kept this vague for a reason, as every clear answer you give creates consequences for other aspects of the magic system, and as a writer you want to have a certain amount of leeway. But there's other uses of the power that are also "talent-based": gateways, for instance. The weave is the same, but when Androl makes a gateway, he can make it really big, despite being weak in the power overall, but some channelers can barely make a gateway big enough the step through. Though on the healing part, there might be more to it. In the current Age, it is common knowledge that healing is a certain exact weave, but when Nynaeve learns to heal, she feels like it's wrong sometimes, and starts to experiment a bit in using all five together rather than the traditional weave with just spirit, water and air. Nynaeve feels like the weave should be different for different ailments as well. This hints heavily at the Aes Sedai of the current Age simply not understanding healing that well.

It is absolutely difficult to relate to Rand's struggle. Farmboy to Demigod having to fight Satan, the weight of the world on his shoulders, Magic-induced madness, nobody trusts him and he doesn't trust a lot of people around him either. Thankfully we have a whole shelf of books in characterization for us to help understand his struggles. Does Rand handle his struggles perfectly? No. But he isn't a perfect person. Some people find that hard to deal with in stories. Many feel like every character has to deal with their issues the right way. But that's not realistic. I like WoT so much mainly because characters make mistakes all the time. And they learn from them. Rand finally coming to terms with the duality of himself and Lews Therin, and finally fully accepting his fate feels incredibly cathartic at the end of book 12, and reading about him in book 13 and 14 is a joy because he's grown so much and he's finally ready to do what must be done, not just out of anger or basic necessity, but because that's the way the people he loves get to live their lives the way they deserve to. Zen Rand is amazing, and the journey towards Zen Rand is the best character arc I've ever read in any piece of fiction.

The Gathering Storm is one of my favourites in the series, so my take might be a strange one to some, but I'd say: yes, it gets better. Sanderson gets a better grasp on how to write Mat. He never really nails him, and he was the first to admit that. He struggled a lot to get Mat's voice and unreliable narrator right, and it shows the most in book 12. Books 13 and 14 feel better: Mat takes more responsibility and generally feels like he's grown a lot and is more competent.