
Originally Posted by
Zero-ELEC
As strong as the plot demands them to be or as strong as will make for an interesting story.
If you want "feats", there's no clear answer as almost every big thing that the WoL faces is done so with the help of the Scions, Adventurer buddies, or some other manner of boost (empowered by the eye of Hraesvelgr when fighting Nidhogg; suffused with the Light of all the lightwardens when facing Hades, only able to control it thanks to the rejoining of Ardbert and the WoL; pushed forward by the prayers and hopes of the Scions on the edge of existence; etc.).
The biggest, baddest, thing that the WoL has faced and defeated on their own is, well, Zenos and Shinryu, and even then it's unclear if the WoL was alone when fighting Shinryu. Certainly they were when fighting Zenos at the edge of existence but how much they were empowered at that point with the wishes of the Scions that they return (after all the edge of existence is more of a metaphor than a tangible place). And even in that situation they nearly died.
In the end, looking at things in a "feats" perspective is reductive, since it dismisses the realities of combat. The WoL, in the end, is still just a person, if you poison them or stab them, they'll crumple like any other, if they get distracted while engaged in combat, they'll take blows like any other. They're just unique in that their soul is more dense and have access to the Echo (and the Blessing of Light besides), and well in that they help people out which makes them liked and then they help out.
People can and will match them martially or mystically.