The advantage of threaded inserts would be to reduce contact between the screws and the mast step? Would that still work for a step with adjustment slots?

From personal experience it took time, penetrating oil, and an impact driver to loosen the screws. Even with patience it tore up the screw heads. I replaced them with stainless hex head cap screws thinking that would make it easier next time using a socket wrench. Not sure now based on this discussion if that was the best choice but I have no plans to move not that the step is where it belongs. I did have to tighten the step soon after when the mast it slipped aft during a daylong spinnaker run in heavy air.