Now this is just a theory, I'm not saying it's 100% true but hear me out.

In skyrim we hear a lot about duels being part of Nordic tradition in skyrim yet the only duels we have so far in Nordic history were between tongues and we learn from Paarthunax that in Draconic society a thu'um match is just a violent, verbal debate and Nordic society has a lot of Draconic elements in it. In most of the first era the Tongues were mostly skilled generals and Jarls and sometimes the combination of both so what I think is that in reality these "duels" were really nothing but debates that nords mistook as dueling and it became further corrupted due to most of Nordic history being passed down through spoken tales and songs and ancient lost and/or vague stone tablets or word walls found only in tombs.

So in conclusion the duels were nothing but debates between political leaders. Also if I'm wrong on the "the only known duels in nordic society are between tongues" point please correct me with a source.