I am sure it would be both cheaper and quicker to recruit from within as opposed to from outside.
A DEC course will be approx. the same time as a RHS to LHS (1 might need a bit more "Easy SOPs" work, the other command stuff).
But the RHS-LHS also involves training a replacement P2, which if low hour is a long process.
Not saying it is right, but that would be the bean counters view - 1 recruitment, 1 course not 2.