In my opinion, though it may seem rather drastic, a good way to fix gem staves is to remove the gems from the gem staff crafting recipes (renaming them to be metal staves instead, so platinum staff instead of diamond staff), add lead and iron staves (and add staves for the HM ores?), then move the gems to make demonite/crimtane and hellstone staves instead. Beyond that, a velocity upgrade or light homing as well as a damage buff could make them on par with the other classes. With gem staves being better and easier to obtain, pre-skeletron mage would have actually viable options aside from skipping progression for a demon scythe.