"Exploitation" ? well, nobody is forced to apply , nor accept the conditions offered.
Unlike some SSTR schemes, this one has ongoing employment at the end (rather than the 6mths/500hrs offered by some) even if the contract is not stunning.
Anyone has the option of doing another profession, or doing the licence & waiting (for however long it takes ) to be plucked from the masses & handed a TR .
I do not defend the P2F / SSTR system, but it is a choice made by the individuals concerned, and has come about because of those preceding them.
In this case any exploitation is voluntary on their part.