I think it's a bit unfair to say the band were completely lost with him. They were just rollin' with it and having fun which is something DS probably helped them to relax and enjoy themselves more on stage.
The first Uncovered disk features some of Derek's best work with the band IMO. The funeral for a friend medley, perfect strangers and carry on my wayward son were from ACOS Ep too but there's some tight keyboard/organs in those songs.
Anyway, Uncovered 2003-2005. Fairly sure those songs are Jordan (God help me it'd make sense if some of them were Derek lol). Anyway, there's pretty amazing organ work in stuff like Heart of the Sunrise and I do believe there's some especially impressive 'hammond' style playing in Since I've been loving You. I'll admit some of JRs sounds have sounded a bit tinny to me on SFAM and LTE in the past, but what really gets me is his creative application of these unique sounds and still manages to make it enjoyable to listen to in the way he uses and expresses said weird sounds. But this 'Uncovered' CD has some amazing styles that you don't normally hear from Jordan.
DS' organwork was pretty good though and he did very well on a lot of the Floyd covers, I thought some of the keyboard textures even sounded more coloured and full than the originals with R. Wright. Also, Lines in the Sand speaks for itself about pushing potentially cheap hardware to it's fullest and making the most of the expressive qualities available resulting in something truly epic.
JRs my favourite player but DS is still a great player that deserves credit but I do think he would have been better suited for a classic rock band
Also JR seems to fit more personality wise into the band, which may not seem to directly relate to the music, but it relates to the 'musical chemistry' that occurs when they're composing and recording.