They did a good job in the ROTS novel. Qui-Gon also didn't disappear like Obi-Wan and Yoda did in the OT, so it begs the question of how the Force Ghost thing works. It's not a mechanical thing because there is no explanation given in the PT.
Qui-Gon dies but apparently can come back (voice over in AOTC, Yoda talks about him in ROTS). Apparently it is significant, but we don't need to talk about. That's not good storytelling.
I guess it felt more like retroactive foreshadowing to the original trilogy more than anything else. It's also not the focus of the story, anyways. I mean, do we need to know what form of fencing Anakin learned between TMP and ATOC to accept that he can fight with a ligthsaber and knows what he's doing? If you thought it needed more elaboration, fair enough.
We don't need the mechanics. We didn't need any of it. The OT had Force Ghosts and didn't need to tell us how or why, that was just what happened when a powerful Jedi died. We can presume the details; there needs to be a connection or a great need or something perhaps but It was just part of the universe. The PT seemed obsessed with introducing seemingly important elements that added nothing to the story. Anakin had to be a virgin birth because. . ?
I think this was to give the character parallels to real-life religion, myth, and/or legend.
Star Wars has always been doing this since ANH. This's nothing new. It's also sets up that this kid is no run-of-the-mill would-be Jedi.
Force Ghosts had to be something new because. . ?
This was largely an accident. Qui-Gon not vanishing after death was realized after the fact to be incongruent with Ben Kenobi and Yoda's deaths. Rather then just writing it off as a mistake, they decided to make a story out of it (and expand on Jedi culture, abilities, etc. at the same time).
The Jedi had to be diminished and impotent because. . ?
The theme of the prequels is falling. The fall of the Old Republic. The fall Anakan Skywalker. The fall of the Jedi Order. That's the story we were signing up to see (esp. since we already knew it was coming).
On top of that, the Clone Wars was a trap for the Jedi Order, and they had walked into it by the time of ATOC, so by the time they realized that something wasn't right, they were not in a position to save themselves.
"Impotent?" Seriously? They sent a team to diffuse the blockade in TMP's beginning, sent the same team back for the specific purpose of baiting the mysterious Sith (Darth Maul) out of hiding by the movie's end, were actively working with Palpatine to resolve the Separatist crisis at the beginning of ATTOC (not their fault he was faking his part), arranged for the Padme assassination attempt to be investigated by their own, were trying to figure out what to do about the rise of the dark side clouding their use of the Force, took it upon themselves to intervene of Geonosis
and got the clone army, by ROTS were serving in the military, decided to spy on the chancellor when the evidence began piling up against him, and acted swiftly to bring him when they realized he was a Sith (and were even working out beforehand what they would need to do if they had to remove Palpatine from office themselves before this). If anything, they were fairly proactive during the movies.
It is just bad storytelling, especially to bring such razor focus to it for a brief moment without any build-up or resolution. If Yoda had declared that Kuat of Kuat told him how to build hyperdrives and he would teach Obi-Wan off screen, it would have been just as bad.
They actually foreshadow it in ATOC. Could they have done more with it in the movies? Maybe. But it didn't come from nowhere. It was also just a throwaway scene that gives a little more closure to Qui-Gon's passing and gives us an idea what was Kenobi was doing in part between the trilogies. It's hardly that important a scene, much less given "razor focus."
I mean, preserving your consciousness through the Force, which in Star Wars is the only path to true immortality--which both Palpatine and Anakin sought (Palpatine for himself, Anakin for Padmé)--was all pretty central to the story of the PT. That's why we needed to know about it.
Did Palpatine seek it or was he just waving it as a carrot in front of Anakin? (In the non-canon Legends material, he did, but that was largely because of stuff written
before the movies. Also, in canon, Palpatine seems to have a different objective in mind).
Also, did Anakin want actual immortality? It sounded like from the movie, he just wanted the knowledge needed to avert a death in a specific case, not living forever.