The problem that you mention is a common one on Dayskipper Theory courses. That said in a couple of ways steps have been taken to address the issue both of poor instruction and of a blindness to the existence of powerboats.
To be able to teach Dayskipper theory courses at night school all you used to need to be was a Yachtmaster Offshore – ie no Instructor training needed and no review of your skills to teach by the RYA. Over the last couple of years all such Instructors have needed to become Shorebased Instructors which has weeded many poor Instructors out of the system.
The syllabus has been reworked this year to include teaching sessions that recognise the existence of fast powerboats as well as slower yachts (historically hardly anything went faster than 5 knots in the examples used!)
This does not necessarily seem to be working though on your course, if you do have concerns about the teaching capability of your Instructor (ie a course should balance the different needs of course participants) then the RYA would be very grateful to hear from you – it is only by doing so that such issues can be addressed. Contact Jon Mendez (Chief Powerboat & Motorboat Instructor) at email@example.com
Should you stick with the course? In my view yes. When I did my own Dayskipper Theory course many years ago it was much as yours seems to be. I learnt lots (and indeed wondered too whether steering to 1º accuracy was possible!) I think the course is an invaluable way to build on the knowledge gained at Level 2 and give a far better background understanding of many areas of boating.
I would agree with Richard regarding using a compass. It is invaluable but your ability to steer accurately to it will vary materially from boat to boat & compass to compass. Steering to +/- 5 or 10º is eminently feasible and can often be a lot easier than programming and fiddling with a GPS. The key about charts and a GPS is to understand how to use them together rather than either or. Methods such as the “waypoint web” and the “railway track” are now being taught to ‘link’ your GPS to the chart. I agree too that to reply on GPS solely is foolhardy – hence the benefit of understanding chart based navigation