You know, the best way to make a character interesting is through interaction. And not just romance and love triangles but with friends or enemies and the like. Humans are a social species and we love seeing people interact in interesting ways.
Which I think is why these two had the bad rep, among other things.
Let's start with Evan and why he was made. Two words; Tokenism and Misogynoir. The former is for needing a black character and the latter is not wanting to aging down Storm for some reason. I can admit when the only reason a character I like exists is due to sucky ones.
A few people pointed out that Evan kinda rarely interacts with the cast and is technically alone in it unless it's a him episode. Like there is Ororo but even then it's undecided. He should have Pietro but they abandoned that concept after their first episode with it only coming up once.
Another reason is that they don't really go into the fact that the Monroe side of the family is kina insane or the sisters' family histories and basically don't even try with them at times. Like it's not like they don't have a lot of material to work with so why didn't they???!!!
Well Evan is an cartoon only character. It's not like they took a character who had stuff going on and basically used him for a love triangle.
And there's Lagaan, the boy they brought for a love triangle. They may have done him better in the last series but the second season will.not.be.forgiven.
In comics, Lagoon Boy was a sweet kid who was a part of the Surface Club. He later joined Young Justice. In YJA, he joined after because of Kaldur who had to fake deflect . Roll with it, it's based on comics. What was his deal? Trying to prove to his king and the others that he's not like Aqualad...
If only. He's the jerkish rebound guy. If you think I'm being harsh, that's what he was. The rebound guy that added extra drama for a love triangle that honestly didn't need it. Like Mgann's morality was enough.
In the yja comics, they give him some depth that was retroactive.
They give him a few scenes with Kaldur but until season 4, that's it.
And before anyone mentions the love triangle, I may be a very bitch who loves watching the world burn, but love triangles don't count for interaction. They're drama and in La' gaan's, used to help keep the couple apart. Maybe I wouldn't be so bitter if they gave him a friend or even a rival outside the love triangle but nope! Rebound guy who's a jerk. That's what they worked with.
The point is that with both of them, they were written to fill a need and it took a bit for them to surpass that. And they still get crud due to the writing.