Spider-Man's first four teammates are this; Power Man, Iron Fist, Nova and White Tiger are all minor superheroes from the comics who had never appeared in an animated adaptation when the series started. Two of them (Power Man and Iron Fist) are quite popular in the comic fanbase and one other (Nova) was gaining popularity due to his major role in the expanded Marvel cosmic universe. This could have been a great way to introduce those characters to a younger audience — but for the most part the series didn't bother, using them as Spider-Man's annoying sidekicks instead, playing mean pranks on Spider-Man and ignoring the fact that he had actual experience. Some improvement was made in season 2, with the teammates getting their own focus episodes, some powerups, and new costumes, but as more teen heroes were added and more guest heroes given spotlight, the original four continued to get pushed out of the spotlight. By the end of the show, they had so little to do it was hard to remember they were ever even supposed to be main characters. Heck, The Hulk had more development than them, and he wasn't even a main character.
An actor example with J.K. Simmons as Jameson. Yes, you have the Ensemble Dark Horse of the Spider-Man Trilogy in this show... and yet all he did was yell "Spider-Man's a menace" without any of the humor that made him a fan favorite to begin with.
The first Carnage. Despite the episode being titled after him, he is here for a few minutes before Harry reclaims the symbiote to become Venom again, and never came back. Hell, when the 2nd version of Carnage was introduced Peter seemed to have entirely forgotten his time as the first Carnage.
Spider-Girl, who appeared in season 3 alongside many other Spider-Men, got this from comic fans due to being simply a female version of Spider-Man (named Petra Parker) rather than the well liked May "MayDay" Parker version of Spider-Girl.
Teen genius Amadeus Cho, well known and liked in the comics for his ability to solve any situation through his quick thinking and for letting the readers get to see the world as he sees it (with calculations on just about everything) is now simply a smart kid whose intellect is not as showcased as in the comics and rather than solving everything through his smarts and quick thinking, has simply become the new Iron Spider.
Any of the "New Warriors" (Spidey's second team) can be considered this, with the exception of Agent Venom and Rhino.
Both Deadpool and Spider-Gwen are Ensemble Darkhorses in this series that fans wish would either appear in more than one episode each (preferably to main-character status) or simply get their own shows.
