A servo motor is better than a step motor. However, the step motor should not leave gaps in your cutlines. If you are referring to dotted cut lines (which make weeding difficult and sometimes impossible) this can be due to several factors.
I have not personally used your specific cutter, however other cutters do exhibit the same symptoms and the solutions are below:
Blade may not be sharp enough. Protection strip may need to be replaced, blade holder may need to be replaced. All cutters will require some maintenance and upkeep including replacement of consumable parts.
Also if you had placed your thread in the vinyl cutting/cutter section, I think you would get more responses to your question.