About Nunez I can't why he could not perform really well but leaving Liverpool to Napoli is good at least he can be a regular starter and he can as well be better than we saw at Liverpool. I believe Isak can fit in any team in the EPL and his form since he joined Newcastle has been awesome and you can agree with me that he is one of the best attackers last season. He is not as macho as some attackers are but he can pass through every defender. In my opinion I would not like Newcastle to be useless next season for letting one of their best go, so who's going to be his replacement for next season? For me is bad and I know their attacking force will never be the same if Isak leaves.
I think Nunez move to Napoli will be good for him to limit media attention on him and even become better.
Any EPL team getting Isak knows already he worth it and they are getting a gem, while Newcastle will suffer a huge lost for their best player, the profit from him would be more than enough to get a player who may do well in same position as Isak but not like him.
I think after Liverpool pulled out such amount for Wirtz, Liverpool should be expecting similar transfer fee requitement for Isak by Newcastle for their most priced possession.