In the 80s at nav school, weak navs in basics were streamed fast-jet on the principle of sink or swim. There was a general expectation that a weak nav could be eased through nav school on to trucks so the swift chop was seen to be more assured.
The same may apply to pilot training. Weak pilots may hack the copilot - 1st pilot route which is what the V-force had in the 70s and the truck fleet in the 70s and 80s.