Gunlaug the strongest sleeper?

Hey I just finished the forgotten shore and is gunlaug the strongest sleeper ever?

In his fight with Nephis he only lost due to being cocky and even then Nephis was probably his worst matchup possible as his echo wasn’t affected by the dawn shard.

Nephis at her peak as a sleeper was a demon with 3 cores, but if she and Gunlaug were to fight a similar opponent I feel as though he would fair a lot lot better 99% of the time (they wouldn’t even be able to damage him so, theoretically he could fight swarms apon swarms of enemies).

If the 2 of them were to have a rematch, with nephis having 1 extra core (if she did gain the extra one after killing him), would she win without him being cocky and tied down by Fate?