He scored 26 and he was their penalty taker. He also played in a weaker league than Serie A and cost up to €100m which is more than Højlund cost.
Not saying Nunez didn't look impressive, but I think your idea of "9 goals" is a bit ridiculous.
He scored 16 in 38 games in all competitions, and a lot of the games, he was either subbed in or subbed out.
However, it's not the goals you should be looking at, but his abilities and a combination of these to understand why he can be a great striker in no time.