Good hacking, with dcamprof json that’s exactly what I’d have done…
One thing to note is that your rendition will depend on both the camera profile and the destination profile. Camera profiles by definition should be linear (putting “look” modifiers in them is sowing confusion, IMHO), and if the destination profile is linear, that’s what you get.
Even if your destination profile is display-referenced in its tone curve, the image may still look “dark”. That’s what filmic, auto-matched, and all that discretionary tone curve shenanigans is all about.
Post a raw and your two profiles, and I’ll run them through rawproc in order to eliminate the extraneous variables…