The problem with "defence" is only based on the "defensiveness" and "thoughness" stats.
GAR suffers from this bug as any other unit does, but the main factor why GAR is a defensive unit is because it is cheaper than INF and offers less firepower and moves MUCH slower. It is still a good unit to defend beaches against seaborne invasions and airfields against airborne attacks. In general, GAR gives you a basic perimeter security that will slow the enemy down - if not defeat him - and gives your reserves time to react. So instead of adding an INF division to every french port you can use a GAR division and move up a motorized reserve if the enemy should attack. You could also use MIL, but these units have significant lower combat power, making them inferior to almost ANY enemy unit that will attack your provinces.
So in general GAR allows you to save up IC and MP and RP, but is still strong enough to defend itself against small enemy attacks, while it offers enough power to delay the enemy until reserves have arrived.
GAR suffers from this bug as any other unit does, but the main factor why GAR is a defensive unit is because it is cheaper than INF and offers less firepower and moves MUCH slower. It is still a good unit to defend beaches against seaborne invasions and airfields against airborne attacks. In general, GAR gives you a basic perimeter security that will slow the enemy down - if not defeat him - and gives your reserves time to react. So instead of adding an INF division to every french port you can use a GAR division and move up a motorized reserve if the enemy should attack. You could also use MIL, but these units have significant lower combat power, making them inferior to almost ANY enemy unit that will attack your provinces.
So in general GAR allows you to save up IC and MP and RP, but is still strong enough to defend itself against small enemy attacks, while it offers enough power to delay the enemy until reserves have arrived.