Kyo said:
May I ask what? I mostly remember Avdol being a non-character, and Kakyoin just occasionally filling Jotaro's shoes here and there for variety's sake (only standing out at the end) -- who himself was a boring protagonist. Someone online once counted and found that there were slightly more Jotaro-focused episodes than Polnareff, which I could not believe. Iggy was cool though...from what I vaguely recall.
Jotaro is actually a lot more interesting and realistic than he seems on the surface level when you take into account his upbringing. His father is very absent from his life and he is a mixed-race child living in 80s Japan, neither of which would benefit his upbringing. The sudden change to his delinquent demeanour from his more boyscout self that's established at the start of the series can therefore be seen as a very realistic way of asserting himself when having so much stacked against him. This includes his attempts at cool one liners, whether or not they hit their mark, which show how much he emulates stars such as Clint Eastwood that he latched onto due to the absence of a fatherly figure throughout most of his life until his journey with Joseph. Along with these, we're shown his more immature teenage side during the Oingo Boingo Arc in which it's revealed he does a dumb cigarette trick that Joseph and Polnareff are well aware of, showing he does like to show off pointless yet entertaining tricks on occasion. By the time of the DIO's World Arc, it's also clear how much he's grown to care for the group as opposed to his more reserved and less concerned nature in the earlier episodes. That said, there's a lot more going on with Jotaro than just being a delinquent Kenshiro caricature. There's also the fan theory he may have Aspergers which may explain some aspects of his reserved nature and the innovative tactics he can pull off, though I won't account for that in defending his characterisation when that's basically just armchair psychoanalysis.
Kakyoin also gets some good characterisation through his actions. Joseph being able to tell immediately that it's the real Kakyoin during the Lovers Arc due to him keeping his uniform on while sunbathing shows how well the group have come to know each other and he often serves the more essential role as the most level-headed member of the Crusaders other than Avdol. There's also random traits to help flesh out his character and interests as well such as his cherry-licking, his sense of humour when it came to Death 13's user and his experience as a gamer.
Hierophants Rise Up The insight into his past at the end of his fight with DIO also do more than the typical last-second characterisation as it instead recontextualises a lot of elements to his prior characterisation, showing that meeting other Stand users allowed him to be less detached when it came to genuine connections and able to form a natural friendship with them, particularly Jotaro who has shown to have found a bond with him due to their shared interests such as Sumo as established in the Wheel of Fortune Arc. There's also the underlying element of him letting himself be controlled and fearful of DIO that is brought up many times in the journey and the irony that Kakyoin's Stand gives him a similar ability.
Polnareff is pretty basic in shifting from serious to comedic when the situation calls for it, though some of his comedic antics can be argued to be a coping mechanism for his sister's death and him being the one to survive so much has the bittersweet element of him regretting doing so when it came at the cost of Avdol and Iggy's sacrifices. Avdol is a lot blander than the rest, though still serves well as a mentor to Polnareff to help him develop in the Hanged Man fight as well as a straight man for the comedy in the Bast fight to make his inclusion more essential, not to mention his attempt at being more comedic and "badass" upon his return possibly being his way of trying to fit in better with the group. I agree Avdol was the least well characterised member of the group. Iggy's arc was simplistic but fine and I don't think I need to get into why Joseph is great.