The Sonic the Hedgehog franchise has had a long and bumpy road with a stunning amount of complete blind missteps. The less-well-liked media in the decades-long canon is hit with a ton of different complaints, but one has stuck around far beyond its usefulness.
By the time of his second outing, Sonic was joined by a second anthropomorphic creature, but the friendly animals didn't stop at Tails. Later games introduced a veritable army of talking woodland creatures, but they never escaped the ire of some detractors. The common refrain of some critics states that people pick up a Sonic game to play as the Blue Blur, not as his countless roommates.
Tails and Knuckles were the obvious selling point in the marketing of Sonic the Hedgehog 2. A ton of the public outcry about the film came with the first cinematic portrayal of Knuckles, and his impressive celebrity voice casting. The film is a success by any normal metric. Already beyond the realm of possibility for most video game movies, both in financial success and audience reaction. Though the film seems to be doing very well, there are still some common complaints that stick with the franchise. When some fans are excitedly buzzing in their seats at every moment of Tails or Knuckles, others find it the beginning of the end for the franchise.
There are a couple of common complaints leveed against Sonic's furry friends. The least helpful one is that they are annoying. People find their tone and presentation to be irritating, even when set against Sonic's too cool persona. Tails is an excitable kid, which is often a type of character that attracts a great deal of derision. Knuckles is a slow-witted fighter, which has become a fairly common trope of ensemble narratives over the years. Those who find Sonic's allies irritating in the games may find that the film has addressed some of their concerns.
The games often sideline Sonic's allies, turning them into little more than a peanut gallery that comments over the action or a friendly face in the cutscenes. Knuckles and Tails are integral to the plot of the film and their presence drives the plot. Sonic, Tails, and Knuckles are the main characters now, so if fans can't tolerate those characters, they aren't likely to stick around for the ongoing cinematic universe.
The other big issue often raised regarding Sonic's allies is that the classic secondary characters, Tails and Knuckles, will open the door for the less well-regarded fixtures waiting in the wings. Some fans shudder at the idea that future films could introduce characters who appeared in the generally despised era of the games. Characters like Big the Cat or Charmy the Bee, who don't have the cultural cache of Knuckles or Tails. These tertiary characters of the Sonic canon appear almost exclusively in group shots or cart racing games today. There's likely a limit on what aspects of the games will make it into the films. The double-edged sword of ensemble casts is that every character, no matter how insignificant or widely despised, is someone's favorite. The other denizens of Mobius could be on their way, but the franchise is still keeping most of its familiar faces well hidden.
Those who still see fit to complain about Sonic's animal allies miss the draw of the franchise, and the giant glowing weakness of the film that hurts its appeal. Because Sonic does have a few friends that would do well to reduce their presence in the franchise, they're the human beings that take up a shocking amount of Sonic the Hedgehog 2's runtime. Tom, Maddie, and Rachel play an enormous part in the narrative of a film that very few people have any interest in seeing them in. Fans who watched the trailer could've been convinced that their trip to Hawaii was a clever excuse to keep them out of most of the action. No one would've predicted, or indeed asked for, the weirdly long-winded fake wedding subplot that all amounts to very little.
Largely unimportant human characters in adaptations of kids' media are an industry-standard feature at this point. While fans aren't particularly interested in them, the studio needs to see some marketable faces to believe a film could be successful. There is certainly some narrative justification for Tom and Maddie's role in the franchise. They're his adoptive parents, and they provide most of the delivery of the film's messages. They don't necessarily need to be there, but it's not a deal-breaker to have them around. Fans will tolerate their presence, but it's not the part of the film anyone is going to be jumping out of their seat to applaud in the theater. The human characters are the most forgettable and least necessary aspect of the Sonic film franchise, and replacing them entirely with Tails and Knuckles would be an unmixed positive.