The writing is not very good. I don’t mean the dialogue sucks, but the writers fall again and again for simple mistakes. For example, in one episode, we learn that grey wolves are being treated better by herbivores. However, in the very next episode, we see the main character, a grey wolf, get harassed by herbivores, contradicting the earlier scene. The biggest flaw of the series though are dangaling threads that never get resolved, like:
Haru wanting to get eaten by Legoshi
Juno’s unrequited feelings for Legoshi
Hyperdrugs
Six Eyes as a chracter
The whole “The person who finds the killer becomes the next Beastar”
Segregation of the students
Legoshi’s “secret”
Etc.
Additionally, the creators introduce interesting elements, but instead of exploring them, drop them immediately. One if the biggest ones is Legoshi’s and Haru’s relationship. We understand that it is weird for a carnivore and herbivore to be in a relationship. However, we never get to see how their relationship impacts their personal lives. Hell, in season two, we never see Haru without Legoshi, so we have no idea how others, like the rabbit girl that bullied her, treat her now. For Legoshi, the impact his relationship has on his social life stops and ends at “Did you have sex with a rabbit?”
Another factor of there relationship that doesn’t get explored properly is that Haru’s instincts want her to get eaten by Legoshi. We see Legoshi training himself to not want meat, but we never see Haru training herself to not get eaten. I feel you aren’t doing something right if Gohin, a side character, gets more screen time and development than the main character’s love interest.
The last big complaint I have is the main plot of season two. In that season, Legoshi tries to find the one who killed Tem. I could never take this plot seriously, because Legoshi doesn’t. He was told to find a killer by a snake, and then he just did. It’s not about avenging his dead friend or anything that results in personal stakes. The writers just wanted him to do this, and unable to think of a good reason, through in Six Eyes to tell Legoshi to go do this thing now. Legoshi has no agency through the entire season in relation to that plot.
I don’t know anything about the manga, I’ve never read it, but “That’s what the manga did” is not a suitable excuse for how poorly written the anime was. The writers of the anime are professionals, they should have known better.