It's not me, it's the industry.
Our local shop, which sells the Duotone Trust c-bar, have sold them to customers that try to use it with their XYZ brand and quickly come to find out their kites back stall, feel different, or simply don't fly the same in a positive or improved way. After too many issues and thus returns, they will no longer allow sales or returns on Duotone Trust c-bars to those that are not using them with Duotone or North kites.
When given the chance they will ask what kite(s) the customer have or plan to have when purchasing the Duotone bar. If they don't have a North, Duotone, or some others like Core and older F-Ones, they sell them Slingshot c-bars since they will usually work well with other low-V designed kites. So far no issues and thus returns with the Slingshot c-bar which is a good testament.
I've had the same experience with several kites that I tested with my North Trust c-bar. Non of my kites were improved or flew just as well, so my experience quite differs from yours. I'm glad you're confident that it can "work just as well or better" in your experience. I'm also glad your technical speak supports my "YMMV" statements since I do know some that have found zero issues and even felt it was better using a high-Y front line c-bar with their low-V designed kites.
However there are simply too many variables with kite designs and rider experiences that play into what can "work just as well or better" for the masses. It really makes no sense to take the risk or deal with the hassle and cost of testing. Just keep it simple and get a c-bar that's designed and works with the kite(s) one flies. If you have a low-V kite, get a low-V c-bar (or one that adjusts) and get out there! Period
I'm also not going to get into the topic of line lengths and angles, but I can assure you I know exactly what you're talking about. Life's too short to explain.