"I was pulled over by a cop because I essentially "cut him off" at an intersection, pulling from my complete stop at a stop sign across the intersection while he, further behind but with no stop sign, was turning into the same road: he therefore couldn't keep so much of his momentum but once he got into the road he needed to slow way down to match my speed."

Apropos of anything else - you DID cut him off, and you did fail to yield (Stop signs are also Yields). His argument about you running the stop sign is invalid, sure, if you were at a complete stop, but if you're forcing someone who did not have to yield to, by your own words, 'slow way down' to match you pulling out in front of them, then you were in the wrong.