On the contrary most maintaintence sparks do little more than clean contacts. They have no clue how to terminate big cables, they cannot design a simple lighting circuit, they would be lost in how to form conduit, cannot design bends in trunking, tray ladder rack etc.
As always there are different cats. of sparks. I will agree an installation spark these days would have no idea how to fault find old time dc/ac motor stuff. But nowadays nor could a maint.spark. Most is pc controlled, and a detail can be obtained from ladder type drawings of any fault. On the whole a real installation spark is worth much more than a maint. spark, hence the difference in wages.