I want to address Darwin Núñez, it was not an excellent season ofcourse, yet Darwin Núñez had a very good season in the league with Liverpool. A young talent, in a new team, in a new country and language and yet he was able to bag 15 goals. We can argue about the fee but it was an okay season for Darwin Núñez in the just concluded season.
Also, with Firmino leaving and Jota always unfit, it makes sense for Liverpool to sign a new forward player
It's true as you said, nunez was not able to perform brilliantly in his first season with Liverpool, but I believe he can maximize the quality he has for the next season. Nunez statistics in the EPL this season, he was only able to score 9 goals from the 29 matches he played, of course that's not enough for us to recognize him as a sticker who is truly qualified so he has to do a better job next season. Jota can still be counted on by Liverpool for next season but unfortunately he often suffers from injuries which make him fail to show the quality he has.
So Firmino departure will indeed leave a gap for Kloop to do in the transfer market. I think he really has to be careful in signing the stickers because they need a lot of big changes for next season after this season their performance has been unsatisfactory because they failed to close the season in the top 4.