They are very easy to kill, but it would be ridiculous to have infantry tanking vehicular weaponry and surviving. I deal with their frailty by packing them into AT-AT's and Juggernauts. However, it does seem vehicles are remarkably accurate against infantry, even at long range. Perhaps infantry can be given some evasion bonus? They can duck to take cover while a vehicle cannot. Also, perhaps grenade range could be increased. Either would make their usage more viable.