The isekai anime So I'm a Spider, So What? has enjoyed rampant success thanks to its unique main character: a spider. The story follows the spider from her hatching through to her struggling to survive the Great Elroe Labyrinth, steadily working her way up to the sun and through increasingly difficult enemies and terrain.
In comparison, the human side of the story feels generic and bland by comparison. It's a standard storyline that doesn't have the risk or reward that our nameless protagonist (named "Kumoko" by the fandom) endures. Beyond that, Kumoko's design and animation are much more charming and unique than the human cast's -- and it's particularly difficult to make a spider cute, but the animation staff managed and have been able to bring her personality to the fore even in scenes where her thoughts aren't heard. The protagonist being a spider in So I'm a Spider is a large part of the appeal, which makes the decision to humanize her questionable.
This is not solely the fault of the anime -- in the original source material, Kumoko does indeed receive a human form, and in every iteration it's to communicate with humans, despite her having the Telepathy skill. It's still questionable why a spider protagonist would become human when their being a spider is the entire premise of the story, but it's a decision made by the source material, not the anime.
This doesn't make the anime blameless -- Kumoko's animation as a human, or even the human/spider hybrid Arachne, suffers severely when compared to her animation as a spider. She goes from lively and all over the place to having the same stiffness as the rest of the human characters. Even her major fight with Potimas doesn't have the same energy as her previous fights, feeling severely downgraded in comparison. Yes her opponent isn't the varied bestiary of the Great Elroe Labyrinth, but that shouldn't affect her own reactions.
Kumoko's limits as a spider were part of the appeal. True, she has to fight her way through the Labyrinth, but it's not a simple hack and slash. She's a tiny spider that barely makes a mouthful for many of these monsters, which forces her almost immediately to focus on being clever and working her way around her own limitations. Whenever she meets humans, she has both the language barrier and the species barrier to work around -- even when she's around humans that treat her favorably, she has the issue of any communication being one-sided. Part of the impetus for the war that takes place in Kumoko's timeline is the arrogant envoy treating her as a lesser being and her killing him out of spite. Her conflict for the majority of the season are natural extensions of her physical shape: she's a spider, so what?
That is why removing this unique aspect is so questionable. As a human, or even a half-human, Kumoko is quiet and reserved in her movements, similar to how she was before being sent to this world. As a spider, she was more proactive and lively. The human side of the story was always the weakest part of So I'm a Spider, and now that both storylines are merging together, we're beginning to lose what made the show so entertaining to begin with.