Val is a utility healer. And she indirectly heals by slowing the monster down. If the team can not avoid it with Tranq’s in them, then that is not Val’s fault that is the team members fault.
The only thing she lacks compared to other medics is self healing but that is the same issue. She is supposed to be played at a height/advantage point. If you are playing her in CQC you are doing it wrong and are at fault for dying.
The heal rate change is to encourage players to switch between her utility instead of staying on the med gun 24/7 and at the same time. Actually make the mastery and the perk to be something useful to her.
So once again. Val might not be equally good at healing. But she is denying damage but with responsibility in the team members hands.