I know of a way that used to work to cause the spawn the next day to contain pike (and the opposite result to obtain swords), worked for all levels of HCs, although im not sure if thats been patched yet. I dont know of any way to force pults/ballis/phracts to go away, but in terms of mech hits, pike/phract/ram is very similar to pike/cav/ram in terms of wave/hero attack/losses, so its generally the pults/ballis causing issues.