andrewr
You seem to be missing the point, hunting through AIP for definitions of priorities and primary aerodromes.
Look at the ML TAC. BLT > EN is opposite direction to V223 H345 Q158 & V126. Ditto various SID/STAR depending on RWY usage. You also have AV arrivals and departures in the mix. You would get the same result opposite direction to the route structure anywhere.
Rather than blame ATC, you would be better educating your students what the air route structure means, route restriction arrows, using ERSA GEN-FPR and how to work within the system of traffic patterns with other aircraft.
Teach them to plan in accordance with the route structure, and by all means when airborne request direct, and the result will either be accommodation if traffic permits, or fly as expected per FPL.
And visit a CEN to give yourself and students an appreciation of ATC's job and issues
