Just some plot details I gathered from various interviews:
>original plot was meant to have Gi-hun and Jun-ho (detective) covertly work together to successfully bring down the death games
>director didn't know how to handle detective Jun-ho and In-ho/Front Man's brotherly reunion so he kept delaying Jun-ho's arrival on the island until it was too late/he ran out of material in the end. Director apologized to the actor for not properly handling his story and promised to use him more in the future (???).
>Gi-hun's self-sacrifice and the destruction of the Korean death games was meant to signify Front Man's defeat. Lee Byung-Hun said he acted out Front Man in such a way that he was both wanting to bring Gi-hun down to his level while quietly rooting for him to win the games. This is why Front Man gave Gi-hun the knife to kill everyone else as an insta-win outside of the VIP's notice.
>director originally wanted Thanos to be the reverse of MG Coin, i.e. looks like a bad guy on the outside but actually good on the inside. One idea they floated around with was had Thanos survived up to the jump rope game, he would've tried carrying Jun-hee (pregnant girl) through it unlike MG Coin
>Gi-hun was meant to survive the games and meet his daughter (literally replace Front Man with Gi-hun in the ending) but director felt he didn't want to leave Gi-hun's story open-ended with him gaining awareness of the American death games while standing idly by
>baby plot was introduced because director decided that "paving way for the next generation" would be an overarching theme

So yeah, S3 was a mess because the director couldn't figure shit out.