Well, sure, you can create more depth and make things more complicated by sacrificing other aspects, that's true. There is quite a bit of supporting characters and I think they did show quite a bit of love to some of them, they just didn't go too much in depth with the ones closer to the protagonist. There is also the fact that there were little episodes...

I watched Arakawa under the bridge and School Rumble, I don't know about Chromartie High so I can't give an opinion about that; but if that's the kind of comedy you like, then it's understandable you wouldn't enjoy Grand blue much. School Rumble has twice the episodes and even another season, you can't compare the sizes of both. Plus there is also the matter of perspective, Grand Blue IS focused on the MC, on what he sees and the things surrounding him and I actually like that fact.

I found out that Cakey and Chise are pretty well fleshed out as characters that perform their role correctly, as well as the two big guys. 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?

There is also a contradiction in what you wanted to see and what the show delivered... Grand Blue is a gag, comedy anime, not a romantic comedy or something that has humor as part of the central idea. 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, remember that this show focuses a lot on the traditional tsukomu of the japanese.

I saw Nichijou recently as per recommendation of Hive account@ascheriit. It's exactly the kind of show you would enjoy as comedy, but there is a catch: EVERY character has comedy in their lives, so they can go ahead and switch characters and focus on the supporting ones because all of them have crazy lives and you can focus on them while keeping the comedy. You CAN'T do that in Grand Blue, period.

There are ways to create more depth in a character even if it's just a comedy anime and I guess my opinion about Grand Blue just doesn't suit it's mainstream fanbase even if I can agree on liking the show still.

If you wanted to say that there are ways to bring complexity and depth to a comedy anime then I DO agree, it's not impossible, but it's not likely when gags are the main selling point. Grand Blue does suit the mainstream fanbase, in fact it's ranked very high (8.2 if I remember correctly) and amongst the most liked this season. I still think it's hilarious, but of course it's not a masterpiece, we've got Detroit Metal City for that, which is also one of the reasons I always make relative comparisons to the rest of the ones airing instead of absolute comparisons... otherwise it would be very hard.

I can't find Chromartie High in my anime download site, though... did you make a typo? I always have time to watch another funny one :D