I think the GTA V soundtrack is absolutely brilliant, such great song choices, definitely just as good as Vice City and San Andreas (and I never thought I'd be saying that) but yes I agree the radio station design is a bit muddled.
I think that the radio stations went through a lot of changes in development and that certain stations were dropped, others were remodelled and that certain songs were kept but moved about through the stations.
First of all, I think there was definitely an 80s station at some point other than Space. Take a few of the 80s rock hits like the songs from Queen, Robert Plant, Julian Lennon and Simple Minds from LSRR and couple them with Wham! and Pet Shop Boys and you have yourselves Absolute 80s, a real life station in the UK I listen to every day (seriously, I hear each of those songs on there at least once a month on there. It's funny because Big Log and Everything She Wants were being played a lot on there in the weeks leading up to GTA V so it was a really nice shock to hear them in the game). I think this idea was dropped in development. I think that LSRR was originally going to be a classic 70s rock station for songs like Photograph and that when the 80s station was dropped, the songs were split up and mixed into the other stations, I think Non-Stop Pop was probably created as a "dumping ground" for songs that came from other stations originally, with others added in to bulk it out. Great station though apart from the modern bullsh*t. I think there's a chance that Space was also created for this purpose, that a few songs from the original 80s station (probably Party All The Time and Give It To Me Baby) were passed onto here and they quickly added a few more funk songs that weren't originally there.
I don't have a problem with this though, I think it adds a good deal of variety to the stations.
I get the feeling that there was probably also a psychedelic rock station at some point, I think that's where Ogden's Nut Gone Flake came from, the rest were dropped and Ogdens was kept because a) it's amazing and b) because it's iconic after the trailer.
I think that there was also probably a jazz station at some point, I really, really love Worldwide FM, but I think those three jazz songs on there came from somewhere else as they don't quite fit in with the chillwave focus it has. Then again, Gilles Peterson does like his jazz so I could be wrong.