How did the local hereditary “chiefs” system differ from an aristocracy since most of them wound up as the aristocracy.
Sounds to me that the Norwegians simply coopted what was there and regularized it as a Norwegian governmental system.
Ya gotta watch those doctoral candidates, always looking for a slight divergence they can claim is a new discovery.
Maybe it's a matter of scale. When northern Europe had tribes, it had chiefs and subordinates. When it coalesced into nations, it had kings and aristocracies.
In the Icelandic Free State, the aristocrats had to compete for the allegiance of the farmers. If a farmer felt that the baron was not offering adequate protection, or was charging too much taxes, he was free to find another baron.