I am not much of a photographer or a skilled photo “developer”, using both RT and dt, a kind of fifty-fifty it is.
Which one to use, can depend on the photo, I am dealing with, on my current mood, on beer available, on fancy new tools in development, and, often, on the hardware. darktable is much more agile with a semi-decent GPU, while RawTherapee is well optimised to use all those CPU cores and threads and stuff.
My first open-source raw editor was the good old LightZone, a proto-darktable in many ways. All those combinations of drawn and parametric masks, multiple module instances etc. etc., transition to darktable brings familiar procedures.
RawTherapee has huge amount of tools and ways to do things, perhaps more than any similar program. (A monstrosity!) Not many users can and do use all of them. With my humble mathematics skills being at their peak in the eighties, I do not understand half of the fine explanations in RawPedia. But this is so to stay, any reduction of dated old features would make somebody disappointed.
ART is optimised, mostly, for the needs of the kind developer. Some improvements have been ported back to RT, many others deserve to go the same way and some will go. As well as ART is made, one RT user will, most likely, sooner or later, miss this and that from RT.
dt and RT are very different and no ideal “combination” will ever exist in parallel universes that we may love more than this often shitty one.
Have all a nice day!