Soulring Ranking
Zayn knew that the three gashes he had inflicted rapidly were not serious injuries. They could be considered light injuries that restricted Merlin's movement a little, but that was already it.
The bigger problem for Merlin was the freezing effect that was passed alongside the three gashes. The Dragontale Twin Sabers were especially powerful in creating a freezing effect around the area they cut. Triggering this effect required a considerable amount of soul particles but Zayn knew that it was worth the high consumption.
The freezing effect caused a numbing sensation around the area of the cuts, further restricting Merlin's movement and the loss of feeling around the leg.
If they would have continued fighting, Zayn was the most likely to have emerged victorious.