As for Cloud. He has no personality or character. He's like a cardboard box. He has even less personality that Lightning who at the start of her game is an a$$hole but at the end of it is a somewhat softer gentler a$$hole who can smile and make jokes. The best moments with Cloud are Aerith screwing around with him because he's such a stick in the mud. After her death and especially in Advent Children he becomes an even worse person.
Cloud and Squall are the type of people who never smile or laugh at anything really. miserable people with messed up developments who never get over themselves or how they grew up.
That's the only likable main protagonist of the PS generation Final Fantasies. He was a fun decent person with an actual personality that wasn't an emo or constantly brooding around who's development was seemingly stunted in childhood.
I'm not seeing how Cloud's just a cardboard cutout/emo/etc. He does come off as a bit of a callous jerk at the beginning of the game, but even that doesn't last long. They haven't even left Midgar before he shows he does care about those around him (why else would he crossdress to get into Don Corneo's mansion, besides the fact that Tifa was in there and he didn't want Aerith going in alone), and he does have a sense of humor (at several points, he says things that he knows will get a rise out of Barret). And even his moment's of being a jerk weren't always completely unjustified. He tells Yuffie that he doesn't care about Wutai's history or her feelings and they just want their materia back. And while you're probably thinking "well, that comment shows that he was still an a$$hole", except Yuffie had just run off with all of the party's materia and they had just caught up with her. And to top it off, she suckers them again right after telling them she's going to give it back to them. And yet, later in the game he's giving her advice on how to deal with her airsickness, probably because he can empathize, since he's prone to carsickness.
This is without even getting into the major character growth he goes through throughout the game. He's definitely not the same character at the end of the game that he was in the beginning.
If anything, in terms of character development, Zidane is probably the worst out of the three. He experiences zero character growth throughout the game. None. The only time he faces any kind of challenge to his identity or shows any real depth to his character beyond being the upbeat hero is when he meets Garland. And when faced with the truth of his existence, that he was nothing more than a literal angel of death, how does Zidane handle it? He ends up acting as "emo" as you say Cloud and Squall were.
If you're not a fan of more serious characters, that's fine. I like FFIX Zidane as a character, but if any PS era protagonist was a cardboard cutout personality-wise, it'd be him.
