If the quality of the graduated cadet released to line seems be a problem, it would be a problem with the training department for not doing their job correctly. If there is a problem with the ex GA skygod captains flying with graduated cadets, it would once again be a problem with the training department for the quality of its command course.
Where I work at the moment, cadets graduate straight to the right hand seat of the A330 or B777. They are required to pass the same checks to the same standard as none cadet FOs. If they can't, they are either retrained or dismissed. The next flight after they graduate may be over the Bay of Bengal in the middle of the monsoon, or to Moscow in the middle of winter. When they achieve 6000hrs, they are eligible for a command. They complete the same upgrade course to the same standard as everyone else or they don't pass.
This company has been hiring between 500 to 700 pilots a year from many years. At the moment they are taking all the ex ryan air and easy jet ex cadets they can get, as they are very happy with the high standard of the product that is produced. At these companies ex cadet FOs may be offered commands on A320s or B737 with as little as 2500hrs.
The best experience for a future A320/B737 captain is to fly a A320/B737 and to be taught how to operate it correctly. Working for a GA company being paid under award salaries, flying antique aircraft VFR may prepare you for the ever decreasing T&Cs of the aviation industry (see the above about buying type ratings etc), but does little else.
If you go the GA route enjoy the flying and the variety and the special locations. Just because you have done the hard yards does not entitle you anything except more hard yards. The world has moved on. If you go the Cadet route be careful hiring a light aircraft for that weekend fly away, as you will have no idea of how those small aircraft work.
The Don
I disagree with your post for a number of reasons. I have experience with cadets in the Middle East and in Asia.
The Middle East was comical at the entry level where the scheme was based on nationalism and wasta. What was interesting, was the end product, which I did have experience with. That is, a cadet who was promoted to Captain.
The knowledge/experience gaps would probably have been addressed with flying experience outside of the airline. I have seen this at both airlines with absurd decisions that would not be expected from pilots with a solid base- for example, both airlines I worked for have seen cadet captains fly an airliner after an engine failure well beyond the first suitable airport.
It is politically naive in my experience to expect a training department not to be powerfully influenced by management! Cadet programs are industrial weapons, they drive conditions lower as they try to take experience out of the equation, and the end product I have seen is in no way near the standard you would expect of a First Officer in an airline which sees safety as a priority. What I am seeing now in Asia, is serious incidents as Captains are overloaded in managing the inexperience of the RHS.
I have cadets sitting next to me with operational limitations such as 10KT X-W and 5KM viz. That gives should give you an idea as to the other gaps in their knowledge base.