BEagle,
Having put nice 6 minute time marks on your chart, and having discovered in flight that the met officer gave you the wrong wind would you not agree that the marks you made are useless clutter for the average PA28 pilot since they were made with the wrong wind?
Personally I favour fixed positions based on recognisable features. You can mark your map once and use it on a thousand flights with different winds. It is also how airways are navigated using reporting points.
The RAF like SCA because in a fast jet it works well as you said. They also favour fixed time marks because they are very interested in achieving a TOT and they have the ability to increase or reduce speed as necessary to stay on time.
Instructors who use SCA or double the error agree on one thing, getting back onto the planned track is important. Thus both are in general achieving the important point of the exercise. As long as we don't have pilots 5nm off track correcting direct to destination then we overall agree.
I believe that correction should be made using the appropriate method within the first 15 minutes maximum.....about 10nm out in a PA28. That takes care of tracking. A Fix close to the quarter of halfway mark will sort out timing.
Remember that a PA28 pilot navigates far better than any fast jet pilot to achieve the same accuracy!
Regards,
DFC