That seems a little strange, you would think if the Foveon sensor was so good at colors, then it would be especially good at sunset/rise!
I would agree with you on Pentax though, I’ve heard very good things about Pentax cameras. The sensor-shift stabilization would be nice to use with my old manual lens which is lacking the modern built in “4-stop” stabilization.
I have heard of both RawTherapee and Darktable, and I tried both of them before I finally took the plunge with Adobe Lightroom. If I could go back, knowing what I now know about RAW editing, I could probably get by with one of the Open Source options, but back then, it was VERY hard for me to figure out what controls did what. If anyone was interested in comparing them, I would recommend trying to find some video tutorials on how to use the specific software and learn to use them before committing to any specific software. That’s how I learned to use Lightroom, I don’t know how I could have learned otherwise.