You said many good things about Vult so it would be a shame if you stop commenting in the forum 
Regarding the sound quality, probably both Braids and Clouds are bad examples to compare. These two modules are mostly DSP based. The only analog parts are the DAC and the antialiasing filters. Those parts should be as transparent as possible. In the case of Clouds, the internals run at 32 kHz sampling rate. Most probably Softube used exactly the same code as VCV to create the modules (the original Mutable Instruments code). If you think Softube version sounds better, my guess is that they added some filtering and distortion to make the sound more appealing.
Sound quality is something I think a lot about when I’m modeling some electronics. Often times the more accurate the model is, the “worst” it sounds and the more CPU it consumes. I quote “worst” because it’s completely subjective; analog electronics has lots of quirks. I always try to strike a good balance between something that sounds good and it’s useful by not eating all the CPU.
In Rack you can find plugins that go from the most primitive sound sources and processors (with aliasing or very digital-like) to very complex and carefully crafted. In Softube you can find fewer but more developed modules. If one would want to compare the sound quality of VCV vs Softube it’s necessary to compare only the very best… and still it’s not clear what should be the criteria used to evaluate.
One realm in which Rack is a clear winner is in the number of people it makes happy.