Done Oslo twice, and would agree lounge food is more of a quick snack and chill with a coffee
The breakfast at the Park Inn Radisson was possibly the best hotel breakfast I have had or was it just the fresh warm brioche bacon and egg rolls and a really good coffee that won the day.
So yeah if your hotel has breakfast it is going to be better than the lounge.
Stayed at Gaerdemon airport hotel the other time, so 7 euro shuttle bus ride (hint make it easy and buy return from machine at the airport bus stop) its breakfast was standard Scandinavian range