Canon: Kent Nelson never looked for another host for Nabu, and just planned on letting him be imprisoned indefinitely. WTR: He looked for another host up to his death, and just couldn't find one.
Probably wrong. He was likely looking for a host when he got abducted, unless you think that the guy who explicitly said that Inza would have kicked his tail over spending money on Xanadu was
actually there to try to speak with Inza. I can't think of any other reason why he'd have been poking around there; if Xanadu was actually doing something morally questionable, you'd think he'd have said something about that since he was taking a super direct approach.
Canon: The Team twice used Nabu as a weapon of last resort; each time, they knew that the price for his help was to be kept as a host, but each time, he let them go free. The third time, he finally made them pay the price. WTR: The Team only got one warning.
Also wrong. The initial fight against Klarion, they had no idea that Nabu had any inclination to keep bodies permanently until
after Wally put on the Helmet. They knew he was kind of clingy because of Kent, but that's as far as their knowledge went. I don't count that as a
warning when it comes off as Nabu playing by rules he never explained to the participants until after they had already violated them. They got one warning total. And yes, I'll admit the Team did use Nabu as a last resort situation and failed to look for a new host as they said they would, but threatening to
take and keep their bodies is simply not okay, no matter how badly those people treated Nabu or whether they "agreed" to it because the alternative was a planetary disaster. Which brings into question whether those "warnings" were actually just extortion, because it's not like it's an in-borne condition of wearing the Helmet. This was just Nabu deciding this was a thing, now, demanding a "price" far out of proportion to the services rendered.
Canon: Zatanna's reaction while watching the news conference that Dr. Fate had joined the League was just to look slightly sad and keep watching. She clearly knew in advance (which isn't surprising, since there was a month gap between the League's decision and its announcement). WTR: The League deliberately sandbagged her, and she had no clue what was going to happen until it was announced.
You may have a point here, but that may also have been a butterfly based on Paul bringing Zatanna to a war conference shortly afterwards. Zatanna being sad instead of angry may have also been her not wanting to seem unstable in front of the Team or something; frankly, the writers should have made that
far more clear if they wanted Zatanna to be learning to move on. As it is, they did
nothing with that: no scenes with Zatanna reflexively trying to punch Batman in the face because he told her that Fate was joining the League, no scenes with Zatanna ranting at Canary about the unfairness of it all until she breaks down and cries, no heart-to-hearts with the Team, even! Just a hand on a shoulder from Robin and one very brief sad look. It's no surprise to me that with the vagueness of canon, Zoat's read on that scene is that the League went super hands-off for some bizarre reason, because did
you see anything about that anywhere in the show? It gets more neglectful the more you look at it, barring the comics which I'll address in the next point.
I honestly can't remember how WTR handled Zatanna's homelife post-Nabu. Wasn't she just staying all by herself in her house or something, without anyone giving a rat's ass about her?
In canon: Batman made sure that Zatanna's affairs were put in order, and offered to have her come live with him. She thought that moving in with a new family would be too much like giving up on her father, and wanted to keep Zatara as her legal guardian and move into the Cave with the Team. Batman agreed, on the condition that she treat him, Black Canary and Red Tornado as surrogate parents until Zatara was recovered. She moved into the room next to M'gann, and zeta-beamed back to New York for school for the rest of the semester, then transferred to Happy Harbor, so she was going to school with the rest of the Team as well as living with them.
In the comics, yes, you are correct, but no TV show should
ever force their readers to read supplementary comics
for crucial character development like this. Based purely on the show, nobody talked about this to Zatanna at all on-screen. Based purely on the show, the League didn't discuss this with Zatanna, either to say "hang in there, we're working on separating them" or to say "How can we help you learn to deal with this".
Nothing. Either the League failed or the writers did, and either way I'm mad. If Bats, Canary, and Tornado were supposed to be supplementary parents, then either they went
way too hands-off or they were never showed doing so on-screen, and if the entire premise of your fic is to highlight the insanity of the decisions made in-show, then what else can you do except take what they showed on-screen at face value (neglect for Zatanna's emotional needs) and extrapolate from there (neglect of Zatanna's physical needs)?
In conclusion, the writers
horribly botched this scenario, but based purely on what we see on-screen, so did the League, because there is a distinct
lack of direct scenes telling us how the League is handling this with Zatanna. Consequently, I consider Zoat's take on Nabu and the League's reaction to him to be closer to what canon actually
is than a more benevolent interpretation that may have been what was actually
meant by the writers. If they didn't want canon to seem like that, maybe they should have explored this more instead of faffing about with episodes like Secret that did nothing for the plot and introducing Rocket for the sole purpose of avoiding "Previously on Young Justice".