Okay, I saw this great big debate on Zero/ZEL and the one thing that pops up quite a bit is that Pulse room where Shelly read the note. I really think you should disregard all of that when judging how good a character is, not because it's unimportant (backstory is very important to some characters), but background info is just background info, not a character. I really hate to ridicule Amethyst and the writers on this, but ZEL is just handled so terribly. I don't think ZEL is a terrible character either.
The whole thing about ZEL is that they're always make an appearance with a pulse and often a different character or pulse is the big focus. Just take a look at the first pulse tangrowth. Yeah we get a glimpse of each one's personality, but it's hard to keep track of which one is which just due to it all being a single sprite. Sure the name changes when a different one is talking but it took me a second run to even figure that out (Lumi is the only one who is easily distinctive due to her more cheery personality). Other than that, it's just a text dumb on pulses giving almost zero insight to who ZEL is. This is the only character to do so as well.
Next event is the Pulse Muk in which Solaris takes the spotlight giving off his no mercy impression while ZEL I can't even remember what they say other than trying to stop you. Pulse Abra we just see ZEL getting aggrivated and the focus is mostly on Lin, in which we finally get to meet the scary leader of Meteor. Again, there's really not that much to go off for ZEL, but we learn quite a few interesting tidbits on Sigmund (and even the snake Sirius has fears).
The only time we really get context of ZEL's character and motives is the Pulse Avalugg. Obviously ZEL had to plant it their which shows signs that someone in ZEL is at least against Meteor and all of this. Eve is likely the one I'm guessing seeing as we don't know much on her. It's so unusual considering ZEL had no problem killing Flo,Amy, and the player at the start of the game when he was alone. If he wanted to lose, he should've let Amy take down Pulse Growth.
That's why when the text dump on ZEL (I really feel that should be something players can choose to read instead of being forced to read through it), I just didn't care. No seriously look at all the little things each character does and look at ZEL and you'll just notice a huge difference in terms of development. The moment you meet Hardy, you can tell he's a very caring person willing to keep trying even when someone is pushing him away as well as the little hatred between him and Fern. That's from a "weak" character. If you want to argue about the text dump Shelly reads, Flo, Amy, Tania, and Julia all have diaries but you don't need to read them to understand or get insight of a character.