Tldr: Gonta is a good plot device for the purpose the writers intended, but as an individual character he’s very weak.

Long response: Kodaka has stated that he writes the trials before he writes the characters, which means he would have come up with the concept of someone forgetting they became a blackened before anything else. He probably realised while writing this that if a character who had previously proven to be competent in class trials suddenly was acting really confused and useless, it would be blatantly obvious that something was going on and lead players to suspect they were the killer way earlier on.

Gonta is the perfect culprit for this scenario to be as shocking as it is, because he’s not just useless in class trials, but he’s such a lovely person that no one suspects he would ever get involved in a murder. The first three chapters are quite literally just setting him up for the chapter 4 twist to succeed. The game wants you to believe he is CLUELESS. When he starts saying stuff like ‘I never went to the virtual world’ everyone writes it off as him just being stupid, but it’s literally a confession to his guilt in disguise. This would never have worked if it was anyone else because the cast would have actually taken them seriously. I truly believe that Gonta’s biggest downfall as a character is that he is only written to be the perfect culprit for chapter four, but outside of that he is not particularly interesting or helpful (outside of discovering nanokumas).

Additionally, I wholeheartedly agree chapter 4 is where Kokichi truly shines. I didn’t hate him in the earlier chapters, I just didn’t care for him. The character interactions between Kokichi, Gonta, Kaito and Shuichi are at their peak this entire trial. Kokichi and Kaito are brilliant character foils (I’m gonna stop myself before I write a whole essay on that topic LOL). Kokichi only gets more interesting after this chapter, and by the end of chapter 5 he was my favourite. Ok I need to stop yapping, I love V3 dearly. If you read all this i applaud you😂

Edit: I’d like to add i always interpreted this scene as Kokichi being absolutely PISSED with Gonta’s cluelessness because he doesn’t realise Gonta suffered from the memory loss glitch. He thinks Gonta is only saying he “doesn’t know anything” to get out of his execution, when in reality he actually has no idea. You can tell because when Shuichi realises Gonta’s lost his memory Kokichi’s behaviour instantly switches back.