Crawford only advantage is about 15lbs… McCallum fought a naturally much larger Toney and was fine enough, I’d pick the “body snatcher” he fought more skilled guys then Crawford, Crawford hasn’t fought one McCallum.
Which can be the version imagined. Utilising this version enhances his perceived speed and mobility too vs a heavier version that may have been coming into the ring. We don't know what Mike was weighing walking up the steps either. Obviously it's not as over the top as Crawford but it's a factor as well.
Given he was reported as being 157lbs on fight night for one of his LWW fights, I suspect you're correct. I doubt McCallum ever weighed within 154lbs in the ring, though. He certainly didn't for any of his title fights.