Its too bad to hear that you've haven't been able to get your car to work right with the new rack. When I did my STI rack, my shop had the car for almost 3 weeks before they were able to get it to work right. They kept at it, figured out the issue, and got it working perfectly.
From what I read, you got a Q-rack, they installed it, you had a shudder issue, so the shop convinced Q-rack to send a replacement. Your shop installed the new rack and you still had a shudder. (sound like the rack was good). You had installed a cooler and it sounds like one of the 4 shops tried eliminating the cooler and you still have the shudder. It sounds like someone suggested your pump was bad (sounds likely) but you replaced it with a stock WRX pump. I would have gone with an STI pump which bolts up with a separate reservoir and having to do some rebending of lines.
So what does that leave? You still have a lot of lines and seals. My guess is at some point in the process one of our lines got a little kinked or a seal damaged. Your rack is much much faster than stock and puts much more load on the system. You need the pump and lines to be working at 100% or you will have a shudder issue.
You can sit on the internet and bitch about your parts supplier, but realistically you should be swapping out lines and seals until you've eliminated parts that could be bad.
Once you've eliminated all the potential bad parts and really really worked at eliminating air from the system, then you get to a point where you can be confident that both racks are bad. Unless all 4 of these shops have completed disasembled the system, inspected all the parts and reassambled, the really can't tell you that the rack is bad. Several of the people that have commented on this thread are quite knowledgeable and I'd trust them as much as the shops you've visited.
Keep at it. You don't currently have the basis to "prove" Q-rack gave you a bad part. Get your car working right because fast steering without problems is rewarding and worth the effort.