>How much better has cell culture yields gotten, and at it's best how does it compare to the GTCB platform?<
Perhaps Biowatch or someone else can help here, but I can’t give you a useful overall figure on the improvement in cell-culture yields because the yield depends greatly on the specific protein in question.
The bottom line—and I think you would be hard-pressed to find experts in the field who disagree—is that GTC’s platform retains a meaningful advantage in production cost for cases other than simple, non-glycosylated proteins that can be made using bacteria.