Nketiah scored 5 goals in 27 games last year. He wasn't a very productive forward. Crystal didn't start the league very well this year either. Arsenal actually lacks a forward like Haaland. The last time they didn't have a forward was probably during the Thierry Henry era. They must be an unlucky team because they've been feeling this lack for a long time. I think they need a forward like Haaland. Haaland scored 100 goals in 105 games for City. A statistic that could make them champions on its own.
Every player in the front line must have the instinct to score more goals because their job is to be able to finish well when there is a pass from their own team mates. While Arsenal's front line players are not like that although I also don't think they are bad because for this season Arsenal is still quite good in the domestic league and also in the Champions League. So they only need a few new adjustments to be able to increase their strength in the front line even though they don't have players like Haaland who always get more support from their teammates.