You're a great mechanic.? You do it yourself and question when you aren't sure.?
You are correct about f/r proportioning valve. If you have not replaced the rubber hoses, they can swell internally and block flow. I just replaced 2 on my Fiero last week for the same reason. Looked ok on outside, wife could bleed with me but kid could not.? Minimal flow through the line. And residual pressure held brakes on causing drag.? Something to look at.