50% chance per entity to die when the vehicle is a bit too high and should be lowered to a more 25% per entity.
This was changed in a patch from (iirc) 25% to 50% to make the use of M3s more risky because they were basically a very cheap hp buffer shield (that could be repaired) for your flamer Engies.
25% can still make up a great variance. So I'd suggest that crashes just deal X-Y% (e.g. 60-75%) max health damage to every soldier inside. On its own it wouldn't be enough to kill them but if they are already damaged from small arms/fire damage against the vehicle, some will die and the enemy can still try to focus fire the escaped units that would now be on low health.
However, it'd need to be a % of max hp because a flat damage amount would either always 100% kill snipers in vehicles or would do too little damage to other units in vehicles.
So no longer would you see outcomes like a M3 crashing but 3 Engineers escaping without a scratch. But neither would you see an outcome like losing a whole sniper squad happen as easily as now (25% chance on M3 crash).
Another alternative could be nerfing Halftrack Garrison cover and decrease the % chance. This would probably also give a more balanced outcome.
Right now these vehicles are basically 360° mobile heavy cover objects (75% small arms reduction, that don't seem to be affected by the close quarters cover denial). Though I am not sure how targeting the vehicle vs. the units inside works, my gut tells me this is another factor that makes it even better than heavy (green) cover.