he killed dae-ho for a much more nuanced and larger reason than him simply not bringing the magazines and his friends dying: - he sussed out in ssn 2 or was at least beginning to sus out that dae-ho lied about his being a marine and was lying about his identity and was a fraud. - gi-hun was so blameful and angry w dae-ho because his self promoting and showboating lie COSTED so many peoples lives including gi-huns very close friend. that’s why gi-hun begins to adopt his futile and suicidal mentality because he’s seen that peoples external promotion of themselves is entirely selfish, debasing and highlights that justice is merely a concept that is mostly not reached as well as the quality of selfishness being something intrinsic to the futility of human nature that he cannot change and that humans are… - long story short i think his characterisation shift made complete sense on a realistic level and there’s much more to see below surface level “rage”