I don't think having little episodes is the problem. Even 3 minutes of screen time can give you a lot of information about a character that would influence how you view them for the rest of the show. Nanaka sniffing Chisa's clothing only took 2-3 seconds and then you'll get the gist of how she would act when the MC tries to do something to Chisa.

I don't think it's really that focused on the MC. We get to see a god-like perspective on the thinking process of some characters in the show while in the moment. The flaw is not taking this advantage to the fullest. For example, that mixer with Cakey and friends. We get to see the reactions on the male side of the story in the moment but we both knew that the women were already oriented about what to expect from the men. I mean, there's a gold mine of info to explore on that mixer episode about Cakey but it wouldn't deviate away from the MC focus.

"You want to know the in and outs of everyone, and maybe that's why you don't like this show; who cares about why Nanaka's obsessed with Chisa?, who cares why the girl is lesbian and an alcoholic?"

Knowing the ins and outs of everyone is the purpose of judging the character based on their value to the show. If I were to ignore their ins and outs then wouldn't that make me more bias about how they are portrayed? Cakey started out as a comic relief but we get to see her motivations she does it because of well done character development. However, the two muscle heads are laid out in love with the ocean and we just have to accept that.

Ana is a bi-sexual. Anyway, I am supposed to care for the characters and supporting characters otherwise there won't be a moment where I, as an audience, would be able to relate to the show. It is difficult to see people's motivations for doing the absurd when you have little to work with and the absurd is something that makes sense to them. It's not comedy when there is no serious element to it.

"Chisa is the typical serious character, what's the point of showing a scene about her working in the aquarium seriously? it would kill the mood"

It wouldn't kill the mood when it was Chisa that nudged Nanaka to take Iori to the aquarium using her connections. Having her own mini screen time not only gives her more depth but shows a prequel to the scene where Iori gets to see the beauty of the aquarium. Part of the tension building. A prep for the punchline.

"You CAN'T do that in Grand Blue, period."

Iori's rival otaku seems like a good candidate for the MC role. We take out Iori and place Kyohei as the one being forced into the diving club and go through all those shenanigans, Iori will not be missed. Why? it's doesn't matter because the story flows are not as rooted to Iori. We get to know Chisa is his childhood friend but not much to go on there. Any heavy connection you could anchor Iori to the show can be replicated by Kyohei's disposition and Kyohei is an otaku which gives it more room for comedy. Between Iori and Kyohei, Iori is the straight man.

I just think comedy done right is when it's done seriously. When you are in an environment where you expect the scenes to be funny, you become easily saturated with the gags that they don't come funny anymore. The fix is to provide novel situations the audience has not seen this one coming. But it doesn't have to be that way all the time. If this gag show taught me something, it's that serious moments in a comedy anime are gems if done right because they show marked contrast in the mood and further adds depth to the character.

We know the two muscle heads are funny but when it comes to safety in diving, their atmosphere changes and becomes a bit more serious. We appreciate these changes more because they act as unusual to the usual of the show and it speaks a lot about their passion for diving (done in less than 10 seconds of screen time.)

Yeah I made a typo, it's https://en.wikipedia.org/wiki/Cromartie_High_School