Grimgor has crossed blades with a TON of characters, but the only one I can think of that directly has a flaming blade is Malekith (though how the Sword of Asuryan scales is unknown as far as i know) and Archaon the Everchosen, who while he fought in their 5-B keys, only Grimgor was at that level and not necessarily his weapon, so should still scale to heat resistance for his weapon, as the Slayer of Kings almost always cuts straight through most weapons and things like they were nothing (including when he was FAR weaker being able to cleave away entire shelves of cursed rock throughout his fight with Be'lakor and basically completely scarring and ruining the mountain they were on), with only a handful of particularly powerful magical weapons resisting it, the same swords flames can burn hot enough to instantly incinerate people into near nothing (limited matter manip level of heat), Gitsnik eventually did break in the fight, but it was only because Archaon basically went super Saiyan and exploded the axe with pure AP instead of him actually cutting through it.
Skill definitely is a factor here as well, as Malekith is superior to Swordmasters of Hoeth who are born and raised to be the greatest swordsmen of Ulthuan and each spend centuries to thousands of years to hone these skills, individually they can slay thousands in melee, while also simultaneously casually deflecting cross bow fire with the same sword, choking an entire river with bodies with little to no effort. Grimgor treated him like a child, and within second Malekith surrendered immediately and instead tried to talk Grimgor out of the fight knowing this wasn't a fight he could win.
Finally, time is REALLY against Travis here, if he doesn't get the kill shot FAST, Grimgor is going to very quickly keep passively amping himself, getting stronger and faster, especially whenever he Waaaghs! which is a substantial spike in power, amongst his other amps.
