The kids being paradox clones
explains any arbitrary difference between them and normal human beings, but that doesn't make them
relatable, which seems to be your complaint. (Similarly, the trolls are aliens, but they're supposed to be aliens of a sort that human readers can relate to.) Fair enough, but being unable to relate to characters on one thing doesn't mean that you can't relate to them on other things. And, as has been noted, extended mourning might not have been all that fun to read, plus it really could have occurred offscreen.
Character reactions to things often seem to be rather weird in Homestuck in that dialogue suggesting negative feelings often won't be reflected on a sprite. I noticed that a lot with Tavros and Terezi, whose sprites are often depicted as grinning regardless of circumstances. Even though sprites with other expressions are available, and I think hero mode drawings of them tend less towards this? It's weird.
As an example, look at Jane smiling normally in
[S] Jane: Enter, despite
looking rather sullen just previously, and with her expressions and dialogue before that indicating that she should remain so for a significant period of time.
I basically have to go beyond just adjusting my interpretation of how the character looks and assume that she's being depicted inaccurately. But it seems weird that I should have to do that with facial expressions. Like, am I expected to make that mental adjustment? It's obvious that I'm expected to adjust re: arms, but it doesn't seem obvious here. Again, it's weird.
The idea that characters can be
undeveloped by getting less screen time doesn't really make sense to me. What does make sense, however, is the idea that they might come to
seem less characterized as one forgets their previous characterization. If I reread Homestuck right now, I'd probably have a much clearer concept of what several characters are like than I currently do.
Hussie has indicated several times that he's more concerned with the experience of archival than serial readers, in no small part because most readers will see any given page first while reading through the archives. This perspective -- that we're watching the formation of an as yet incomplete story -- is worth bearing in mind. And if you find that reading the story as it forms interferes with your enjoyment, it might be worth considering just waiting a few years for the thing to be finished and then reading it all at once.
Essentially, only getting a little bit of the story at a time doesn't allow one to see how it "really" is, it
prevents one from seeing how it "really" is, because of the two ways of reading it, it's "meant" to be experienced more like a movie or a novel than like a television series. Or rather, of the two ways of experiencing Homestuck, archival reading is the
more intended one.
Also, bear in mind that Homestuck updates a
lot more often than a normal webcomic. Like, tremendously more. So much more that a normal webcomic focused entirely on OMG EPIC PLOT would probably output
less epicness, in absolute terms, than Homestuck does. So we don't get any less of that, we just also get other stuff in between. And this other stuff allows us to get to know the characters and their relationships with each other and makes the OMG EPIC stuff seem all the more impressive by comparison. Because there's just these kids, see, doing all sorts of relatively unimportant and mundane things, AND THEN SUDDENLY ALL SORTS OF CRAZY **** IS HAPPENING OH MY GOSH WOW WILL YOU LOOK AT THAT!
But just as the relatively mundane may make the spectacular even more exciting by comparison, so too may the spectacular make the relatively mundane more dull. And the relatively unimportant stuff can crowd out the epic stuff in your overall impression of the story, and some readers may not like that. They may wish that they could skip the "boring parts", but the "boring parts" are necessary to really understand the exciting parts, and thus getting through them may seem like a chore. I personally do not find any part of the story to be boring, but hey, that's me.
I hesitate to recommend Homestuck to anyone who doesn't have plenty of free time, both because there is a lot of it, and also because a lot of people seem to find the beginning to be unappealing. (I didn't, but again, that's me.) For a lot of people, it's probably not really worth it to slog through a lot of stuff that they don't care for to get to "the good parts". "Thousands of pages of kids arguing with each other over the internet, mostly? PASS!" That's a legitimate response!