Welcome to real combat.
Pinning is not a way to kill the enemy but to protect yourself. So if the enemy is pinning over and over, he's not killing you. Since you're behind cover all the time. So why is he bothering? He should be trying to _flush you out of cover_, not _force you into it._
"as this takes quite a bit of ammo"
Actualy by RAW you can Pin people with 2 laspistol shots a round.