I think most people who premade would agree with you on this one. It would be nice for groups of 5 to only run into other groups of 5, fill the rest with pugs.
If it meant longer queue times that’s understandable and might even push premades out of the unrated content into something more competitive.
The problem is though, BGB has killed the RBG scene which was already on the brink of death. The symptom of this is that lots of people who should be doing RBGs will just play Random BGs now. There are a lot of factors at play here and why we have ended up in this situation.