Great point and your "rant" is surely appropriate. Who the hell swaps in disc brakes so that the car stops worse? What person would do this on purpose?

I can see and have personally endured situations where a conversion has been assembled using a bunch of unrelated, non stock parts. Sometimes it all works, sometimes it sucks. The "advantage" of installing a packaged kit from a reputable source is that it comes with the expectation of safe and proper performance. The buyer assumes that the parts are engineered to be a better setup as compared to the stock drum brakes.
I'd be pissed if I spent $$$ and the brakes still sucked.

Years back, I was running a 292/509 cam in my 440/493 70 Charger. The low vacuum made my low speed braking what could be best described as "LESS than optimal". I thought it would be a good idea to switch to a manual brake master cylinder. HERE is where things went awry...
My whole setup was pieced together from various sources. I had the mid 70s style 12" front rotors, the 2.6" single piston front calipers but then a 10.7" rear rotor with a 1.5" rear caliper. I had a few manual brake master cylinders here of different bore sizes. There is no shortage of info online regarding what effect the bore size has on pedal feel but I decided to try things for myself. I tried the biggest bore first, I think it was 1 and 3/16".
It was horrible. It felt like the brake pedal travelled hardly an inch and the car felt like skidding tires on wet ice.
I tried an 1 1/32" and it felt about the same. The 3rd one was an iron 15/16"unit. It felt okay so I thought I was getting close. I called Dr Diff and he suggested an aluminum 15/16" MC he had in stock. I installed it to find it felt about the same as the iron one of the same size.
I started reading here and elsewhere about bore sizes, pedal ratios and such, all in the hope of making a NON power system work for me. I was on a deadline though. I needed he car to be back together for The Spring Fling in Southern CA. I ended up wussing out...I put the power booster and 15/16" setup back on along with a small vacuum can.

Some time later, I took a spare brake pedal and drilled the pushrod hole 5/8" higher then welded washers around the hole. This affected the pedal ratio, reducing the pedal effort. Days later, I saw that I had a DISC/DRUM proportioning valve in the car! What ??? All along, I should have been using a drum/drum distribution block.
4 wheel drum AND 4 wheel disc systems traditionally rely on the wheel cylinder or caliper bore sizes to determine the proportioning. The power booster was masking some of the incorrect proportioning so without it, there was simply not enough force.

All of the mish-mash and mistakes I've made have at least helped me learn. I suspect that if I tried swapping in the manual MC now, I'd have better luck with it!