upto a point.
if you keep shield static and plot a graph of def% vs Mitigation and absorb% vs mitigation, you will see that specially for an assassin, def stop being better than absorb at somewhere around 27%ish
There are 2 variables in play. You can't look at them individually. I do know that absorb has more relative value for an Assassin thanks to Dark ward. But point for point, Defence should come out ahead assuming equal points in each. It's also worth noting that, since Defence is rolled first, higher Defence chance lowers the worth of Shield and Absorb,