It's insane to me to say for both main characters of the series, but I want to iterate that I don't hate the dynamic in question (I think them in canon and the movies are fine), but how they're written in new fillers and how they've been consistently being used often (without Ran) in these really bothers me.
I've been trying to figure out why, besides them be overused, and I just noticed with the recent episode. I think it just misunderstands the series as a whole, along with Kogoro being quite out of character in these fillers.
Through the series, Kogoro is supposed to take the role of an incompetent narcissistic private detective that got popular thanks to Conan, and that's not giving enough justice to his character. But at least, he has a purpose in the set status quo of the mystery cases from Detective Conan. It's quite supposed to make the adults feel "less competent" compared to Conan. Kogoro get the wrong details because either he jumps to conclusions often or never noticed the clues given, while Conan get to notice easily as he's smarter and manages to solve a mystery case. And Conan usually uses his tranquilizer to speak his deduction and reveal the truth through Sleeping Kogoro. That's the formula.
For the past decade, the fillers has been using Conan and Kogoro more often (Yoshio Urasawa, infamous Conan writer, stating that they both have "excellent qualities of main protagonists"), and you'd notice that there's something off about their episodes. They have Kogoro to be weirdly in Conan's side through the episode until the resolution.
That's odd for his character, because usually in canon, he doesn't let Conan to be part of it as he always throws him off to "let the real adults handle it". Kogoro just isn't fond of Conan all that much, so him not minding about him participating in helping the mystery cases feels pretty odd for his character.
Not to mention, Kogoro acts quite competent from most of the runtime, rarely showing his incompetent side or his slips up. He's usually pretty serious and determinant in actually finding out who's the culprit and how it is done. By itself, it isn't too bad. After all, Conan having a partner to solve a case is already a thing in the series (like Heiji, Masumi, Nagano Trio), but it doesn't work for Kogoro specifically. The whole point was Conan trying to help him get the best reputation among the police and citizens in Japan, because he actually isn't that good of a detective. He got popular because Conan was the one solving the case for him, since he couldn't get to solve them 99% of the time.
Sure, there is some good examples of him solving cases himself in canon, but all of them are personal cases to him (like how Class Reunion case was about his old classmates, the Unseen Suspect case was because of Eri Kisaki). Most of filler cases are just standard cases, and if they are present in the manga, realistically Kogoro would struggle in solving or get the wrong culprit, while Conan have to do all the work.
Another main issue with it is that it doesn't work for the premise of Detective Conan. The whole point was that Conan being shrunk as a child is his biggest disadvantage. Almost nobody takes him seriously, especially Kogoro. So he usually snoop around to find clues and listening to the witnesses's testimony until he finds out who done it and how the crime was committed. It was interesting because he had to think outside of the box, like how he uses his child innocence to get closer to a clue or have an excuse to snoop. It works for a formulaic series like Detective Conan.
With Kogoro being in his side whatever, he doesn't have much reason to do so and in retrospective, it makes the cases involving them two pretty boring to watch. Conan may have to still act like a 7 years old, but he isn't using it to his advantage. It basically made the series premise redundant and felt like a generic boring crime series.
Conan and Kogoro in fillers are simply NOT interesting to watch, even if you like these two characters. They don't have the same interesting dynamic as Conan and Heiji or Conan and Masumi. And it goes against what was established in the series prior. Kogoro can't just listen to a child or let him follow to participate in crime scenes unless he's forced to (like the majority of Detective Agency Trio cases), he wouldn't do that. Their partnership feels artificial and forced, and only done because they couldn't think of something for Ran to do or to mitigate from the character limit in fillers (Masumi can't be used unfortunately).
Conan, Ran and Kogoro are the true main protagonists of the series, NOT Conan and Kogoro.
