the sniper rule was your problem, not the healing. in such cases either have a taunt to draw the fire or high speed (for range) and high life (magic) or some kind of void card with no meelee in second/third position to protect the low life archers. also with the sniper rule it pays out to have a triage monster further back.
your opponent went for high speed with decent life in second position and most of the archers missed because of that.