I just got my Forum Cut GSC dry enough to try a bit, and I think I may have found part of the answer. My head was (almost)perfectly clear, but the body high was noticable. The anthocyanins found in purple weed is supposed to be good for pain, not necessarily good for a high as a terp isolate. Obviously the GSC isn't blueberry, but I think the theory is sound. I think a weaker body high might go unnoticed by us high-tolerance types.
I am all about the terps, but the stinkier the better. I think the foulest smelling stuff has undertones of all those other flavors. Some flavorful terps do nothing for the high but add to the overall experience. Isolating for those specific terps out of a flavor goal is probably cancelling out some of the good shit.
I also think that a randomly occurring blueberry (or other sweet varietal) pheno in a dank strain will necessarily be more potent. Which is the draw of some of the elite/heirloom cuts - and the thing that can't be reproduced easily in seed form.