Thirdly, there's nothing stopping Miles from relinquishing his role as voice actor to someone who actually has training of voice acting. He can get Kerry to write Jaune instead. No, Miles Luna gets no benefit of the doubt from me. As far as I'm concerned, he's still basically Sokka but shit.
I wouldn't really compare Jaune to Sokka because... Sokka is legitimately entertaining, and becomes a badass towards the 3rd quarter of the series.
However, I kinda have to echo your sentiment there. The one major thing that doesn't make sense, and needs to be fixed over almost everything, is Jaune and his presence into Beacon. He doesn't know what Semblances are, he can't fight, he can't make and maintain his own weapons. His motivations for getting into Beacon are not really clear from what I understood of the first two seasons of the show. He's just kinda there, and can't even do what's expected of basic Huntsmen. He also has a really boring character arc that isn't even resolved all that well.
On the flip side, Ruby despite being 14 gets a pass into Beacon because she's
incredibly good for her age. She received training from one of the best Huntsmen in the world and she is skilled at forging and maintaining her own weapons to boot. She sucks at hand-to-hand fighting and is socially awkward, struggles with her confidence, and has very little practical experience, but that gets better over the course of the show.
Sokka actually has a realistic reason for being so bad at fighting. He's a boy trying to be a man in his father's absence, and has received little to no basic training. Throughout the series, he begins to feel downtrodden about being a burden to the group, because he feels that he can't compete with benders. However, he's shown to be a quick learner and learns various fighting techniques throughout the series, which ultimately culminates in him becoming an trickster swordsman as he distinguishes himself from the group.
Meanwhile, I can't really say what distinguishes Jaune from the rest of the cast RWBY. They try to play him off as a strategist and leader, but it just comes off as subpar--at least to me--because it feels like he's chasing behind Ruby's character--who is the strategist and leader of her team. It makes the character dynamic a little strange in season 4, because you have two characters with the same role in the same team now and to me it just kinda doesn't work as well.
Roosterteeth should have taken a page from underdog stories. Make Jaune the Deku of RWBY. Have him enter Beacon on special recommendation from his parents, who want to prove that a Semblance-less Huntsmen can make it. Have Jaune be an incredibly skilled and smart fighter who is largely hampered by his lack of a Semblance, who has to deal with the scorn of his fellow Huntsmen because they all see him as a burden. Give him weak aura, to the point where he needs to wear a special armor that strengthens it. Because of his past of being ostracized by his peers, he could have an outlook on life where he doesn't really care about status or titles, which would tie into his connection to Pyrrha who is often seen only as a celebrity and wants people to see her for who she really is.
Make his story arc about him learning to lean on his teammates, as he has always had to do everything on his own. This would distinguish his story from Ruby, who is trying to learn how to be a leader for her team. As for his fighting style, make him a trickster like Sokka who fights dirty. Have him use dust crystals like grenades and bombs as he manipulates opponents into his traps. You could make him interact with Ruby a lot, asking her to design various gadgets for him to use. The best thing about this is that you could do this while still giving him his dorky personality.
I mostly just watched the first two seasons of RWBY though. I sorta lost interest in the show after Monty died.