it could be either. If you have a multi meter you can OHM test the cables. Excessive resistance would cause the start to not get enough amperage. So what I would do is test the resistance of the good turning over engine cables to get a point of reference for about what they should be then test the slow cranker. Or IF they are easy to remove swap the starters on the motors, if the slow crank moves then the starter is the problem. I try to help as best I can, I am new to PWC's but have been a mechanic for years, the mechanical aspects are pretty much the same.
You also may want to see how it turns over by hand with the spark plugs out to make sure she isn't seizing up.