@Aleph to be clear, the input profiles in RawTherapee are designed to give accurate colors. This is not the same thing as aesthetically pleasing colors or colors with a certain “look”. “because DPP got the best colors for my camera”, this is likely a result of DPP using a tone curve + a color mapping which gives a certain “look”. You can manually do the same in RawTherapee, then save the settings as a default PP3 for raw files. For example when working with skin one generally wants to smooth-out red splotches and shift reddish colors closer to skin colors (e.g. using the Vibrance - Skin Colors tool https://i.imgur.com/Fk0BgAM.jpg ).
RawTherapee first checks for a DCP input profile when opening a raw. If none exists, it looks for an ICC profile. If that does not exist, it uses hard-coded values from dcraw. As RawTherapee ships both an ICC and DCP input profile for the Canon EOS 5D, it will use the DCP by default. You could select the ICC manually https://i.imgur.com/c3R6Luh.png though it looks almost identical to the DCP.
Do you have a color target like the X-Rite ColorChecker Passport? If so, if you shot it under daylight and tungsten light I could improve the DCP.