Arthurian myths are vague, as there are so many different versions. The original tales they're based on are more wild, whilst the later retellings seem to be more grounded.
In any case Arthur is still a good high example of a high level fighter, whilst Beowulf is another one. I see them as two differnt progression paths from the same roots. One evolves to become a leader, and the another evolves to have superhuman capacities. When gamified, I can see both being viable.
This is also why I don't want warlord to be a separate class, I want it to be something a fighter can become, like in how old school D&D fighters often evolved to be leaders. Same with "superhuman" warrior. One issue with the fighter is that if anything that is more involved than hitting things mundanely with sharp sticks gets spun into separate classes, so there is no much room for the fighter to grow.