Many fans feel this way about Donald, since one of the big draws for the reboot was that he was supposedly going to play a bigger role this time around and he has only appeared a handful times so far since the pilot, with some of those appearances being brief cameos. It's since been explained by Word of God, and subsequently confirmed in The Last Crash of the Sunchaser!, that he was spending most of his time working on repairing his houseboat so he and the boys can move back to the marina. Frank has said we will be seeing more of him in Season 2.
While he did get more screentime in the first half of the second season, he was notably Put on a Bus for most of the second half, leaving people split on how whether his somewhat bigger screentime in Season 2 made up for his lack of screentime in the first, or if it was just more of the same, especially when given his relatively small role in the finale. Season 3 made some effort to rectify this like giving him more focus and development (especially with the introduction of Daisy and Goofy) like Season 2 only this time he doesn't get Put on a Bus, and he played a much bigger role in the Grand Finale.
Fans loved the new take on Mrs. Beakley by giving her more of a bodyguard-type role, but aside from A Day in the Limelight in "From the Confidential Casefiles of Agent 22!," most of her appearances in the show have been minor, and she's had the same amount of screentime Donald has, namely not much. And unlike Donald, she doesn't even have an excuse for all her absences, and her screentime in Season 2 has remained limited.
It gets even more evident in season 3 where despite F.O.W.L (who was a past enemy of hers from her time in SHUSH) being the main antagonists that season, she still barely got any focus that season only playing a major role in three episodes and appearing in the least amount of episodes that season among the main cast at only eight episodes total.
Gabby McStabberson made a huge impact in the pilot as a badass Dark Action Girl with the mellifluous voice of Jennifer Hale, and promptly disappeared. She finally showed up again in the Season 2 finale, but without any lines, implying a major reason for her absence is they’ve been unable to get Hale back. She finally speaks again in "Louie's Eleven!", but it's to start talking about a backstory and motivations that get cut off by Webby and never elaborated on afterward.
Negaduck (aka Jim Starling) hasn't been seen since the Cliffhanger ending of "The Duck Knight Returns!", and Launchpad and Dewey still haven't learned the truth. He's still lurking around in the shadows somewhere, plotting revenge against Darkwing which has yet to be unleashed...noteWord of God has it that they couldn't fit him anywhere in Season 3 cause they felt he deserved better, and he was supposed to be in "Let's Get Dangerous" according to storyboards. However, with the show confirmed to be ending after the third season, this means that, unless he is planned to be involved in a recently announced Darkwing Duck reboot by Seth Rogen, he'll likely never appear again.
Many of the recurring villains present throughout both of the first two seasons have become sidelined in season 3 to make way for F.O.W.L. While Magica de Spell and Flintheart Glomgold served as major arc villains in seasons 1 and 2 respectively, and both got two episode in season 3 where they played a significant role in the plot (with the former progressing the Myth Arc in one of her episodes due to her connection with one of F.O.W.L's operatives), Mark Beaks has only had one focus episode and two brief appearances in others, and the Beagle Boys had a minor appearance and with Ma Beagle only given one major role in an episode.
Huey Duck. Compared to his brothers he's drastically underdeveloped and gets far fewer moments to take the spotlight. To make matters worse, while Season 1 was focused on Dewey's story arc of finding out about Della, and Season 2 on Louie learning not to be greedy, Season 3 did not focus on Huey so much as on the Missing Mysteries and the McDuck family's feud with F.O.W.L. and only a handful of episodes centered on Huey. Even the final two episodes before the mega finale were once more focused on Huey's brothers, with Dewey learning not to be reckless or put people up on pedestals (though Huey got Dewey to realize that lesson) and Louie learning to take responsibility for one's mistakes, and in the finale itself most of the attention and development goes to Webby.
Gladstone and Fethry barely appear in the show (they have exactly seven appearances total, one of which is a cameo) despite being major characters in the comics, as well as Donald and Della's cousins. It's debatable which one of them has it worse - Gladstone for having the potential for interesting Character Development and never getting involved in the Della Myth Arc, even though no reason is ever given for why Dewey and Webby can't just ask him what happened to Della, or Fethry for never playing a major role in any episodes outside of his debut and his quest to become a scientist never being followed up on.
Out of all the characters from the Disney Afternoon who appeared, it's widely agreed that the Rescue Rangers were the most underused. Unlike the other characters, who were the focal point of their episodes, the Rangers come off as being more of a Chekhov's Gunman, appearing as Black Heron's experiments, who Launchpad helps escape, before they return at the end of the episode. While it was sadly understandable, as the Rangers had to be snuck into the show in the first place, many fans were hopeful that they could have had a larger role in the finale, much how Darkwing had a decent role in "Moonvasion!". Instead, they were reduced to two cameos, one of which could easily be missed.
The other Beagle Boys from "The Beagle Birthday Massacre!" and Black Arts Beagle from "McMystery at McDuckMcManor!". With all their different cliques, they would make interesting antagonists and potential allies or enemies to their ordinary brothers.
It would have been totally awesome if Daisy Duck got to participate in some of the Duck Family's adventures, and we could have seen a few more dates of her with Donald and maybe interactions with Della Duck and Gladstone Gander. Unfortunately they did not do any of this before the show ended.
Given all the shoutouts to The Disney Afternoon that were made in the show, and the reimaging of several of the characters from said shows, it's rather unfortunate that the cast from Adventures of the Gummi Bears never got anything more than a cameo in one episode, with their MacGuffin having more story significance. Yes, they were established to have existed years ago, but it's not like time travel isn't canon in the series. And though the show usually recasts the voices at least twoof the actors from the original series note While Paul Winchell did voice Zummi for most of the show's run, Cummings replaced him during the last two seasons after he had a stroke, as he did for Tigger on The New Adventures of Winnie the Pooh. worked on the show, so all in all, it seems like a wasted opportunity.
This show's incarnation of Dijon (here D'jinn) presents him as The Comically Serious noble warrior of genie ancestry who could had help the Ducks during their adventures in the Middle East or as an ally against F.O.W.L. He however only appears in two episodes of Season 2, and only gets a mention in one episode of Season 3.
