Soulcast permanent bridges between the plateaus? Make some rock ones just like the Soulcast barracks. They would still probably need bridges for the final assault, depending on where the gemheart was, but they could move much faster beforehand than they did. That speed would have meant they wouldn't need bait most times anyway (and Sadeas was the only one mentioned to use bridge crews as bait, though others may have copied him later).

And then, instead of just Soulcasting bridges, they could have Soulcast over entire chasms, making large areas that could be used as warcamps. Eventually, they could press on through the shattered plains, moving easily.