i think the throughline with these four is that they don't develop, at least not in the way you hope they will. you want equius to stop being so concerned with his place on the hemospectrum, instead he allows and takes pleasure in gamzee strangling him. you want nepeta to stop being so naive and impulsive, instead she runs in to defend equius with no plans and gets killed. you want eridan to get over feferi and feferi to not have to worry about eridan anymore, instead eridan goes crazy with obsession and kills feferi. and the fact we barely see them again after this makes it hit so much harder, the idea that these four are just sort of permanently at their lowest points after dying, at least as far as we can tell.