I think you are too quick to jump to conclusions because as far as I can remember Nunez also did it last season when he first joined and had pre-season games in fact he scored 3 goals in one match, but after a real season his performance continued to decline and Klopp defended him then said he needed more adaptation. We know Nunez has great potential but besides adaptation he also needs the right partner, this season Liverpool have brought in Dominik Szoboszlai this is Liverpool's attempt to prepare the right partner for him and we have to wait for the official match once the season is running.
Pre season games help players to adapt and understand the players and teams style of play but it doesn’t guarantee how a players performance will turn out, we have seem a lot of players perform wonderfully well in pre season games and end up becoming a flop when the season begins. Nunez is the best example, his pre season performance was excellent and he was even compared to Haaland and some even went as far to say he woulf beat Haaland to become the highest goal scorer in the league. No mistakes Nunez has got qualities and he could make a turn around when new players joins the team, last season was not a good season for the team and maybe that was part of the reasons his performance declined.
For all that says he needs time and those that say he needs to play with better players we will see the outcome of his performance next season because the team have added some quality players and by now am sure he would have fully settled, one season is enough for a player to adapt to change. I don’t know what others may think but as for me his performance this upcoming season would determine what i will conclude about nunez. He need to prove everyone wrong and redeem himself.
To me, most of the preseason games are glorified training matches and that's because most of these club players doesn't bring out the best from them when playing these preseason matches because the games aren't important to their respective clubs and the goals scored in the preseason games doesn't get added to a footballers record.
That being said, most of the English Premier League clubs has shown that they'll do extremely well when the new premier league season kicks in August
True alot of players play these preseason games with no pressure at all which is why their best is not seen in these games only newly promoted academy players that want to impress and keep a spot in the team actually play to their best. Preseason games are not important games thats why it is played with less effort, it is used to assess players and to blend the team so all players get familiar with each other before the commencement of the league. Irrespective of the goals scored I don’t usually use the preseason games to judge players and the team, some players do well in the preseason and fail to perform well under pressure when the league starts while some others play averagely in preseason games and end up having a wonderful performance in the league when the season starts.