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No, I don`t feel the Vikings [Norse] were overrated. To an extent I feel they are probably underrated.
In regards to their abilities as warriors, I think you need only look at the lands they settled and held, none of which was done by saying "please"..from Dublin, York, Normandy etc..we all know these things so no need to list them all.
They acted as personal bodyguards to the Byzantine emperors and fought in their armies [ Varangian Guard] obviously because they were seen as able fighters. I know a little politics was also at play, they were seen more trustworthy because they did not have a personal claim in the land, but this alone would not be the reason they were chosen.
They took part in the Byzantine naval expedition 902 and 949 to Crete and fought in Syria as part of the army 955.
Here in Ireland you recall the famous elite mercenaries, the Gallowglass. They were highly prized by the Irish chiefs [who themselves were pretty good fighters!]. These Gallowglass were made up of Norse-Gaels from Scotland. The Irish chiefs employed them also as bodyguards and personal aides
To be used in this manner, must surely be evidence of their fighting skills.
On a final note, remember the Beserkers. They fought to the death and worked themselves into such a frenzy that even after battle their own companions could sometimes not approach them until they had cooled off [ probably drug related]..