First off i understand the PCML/NLAW is a lightweight system and not expecting it to one shot a tank, but an aimed shot into the rear/sides/turret of a BTR (APC family of armor, marshals, tigris AA, panthers) should result in a mission kill whereby either turrets or gun systems should be damaged and not just the tracks/wheels and said vehicle simply turning around to kill the player.
the issue is much more obvious when attempting longer ranged attacks in crosshair off modes whereby the player has to range and lead the target only to see the missile hit the rear or the vehicle while it drives off into the distance raining fire on the now stuck player as the reload/weapon change animation comes on.
obviously a low hit would not affect the vehicles much but a well placed shot into the rear or turret/gun systems should do more damage and force the crew to retreat or bail from the vehicle. A similar shot by the RPG42 with the appropriate anti armor rocket deals sufficient damage to force a bail or even destroy the Kamysh so why should the PCML deal such insignificant amount of damage? This forces most players to depend on the titan's lock and kill or use the RPG42 which doesnt help with immersion
TL,DR: PCML should by able to reliably damage(not destroy) APCs/Tanks from side/rear/turret hits particularly more vulnerable systems like guns/turrets and not just deal some track damage and get the player killed in the next 5 seconds