Keep in mind that each test is evaluating a different part of the system. Unless the motorboat test was evaluating system power (rather than say, tracking a slowly moving object, identifying objects, etc) then the time to burn through might not be important.
Creating a powerful laser is hard. Identifying a craft, understanding which part is best to target, and keeping the laser on that spot on the moving target is just as difficult. You can't expect a human to be able to do it like a video game - not for missiles, anyway.