Hard to think of many examples where Liverpool forwards suddenly come good after a few years.
Owen, Fowler, Torres, Suarez, Salah, Mane all looked the part straight away. Firmino struggled first few months but that was a coaching issue - as soon as Klopp came in he proved his worth. Suarez in the sense that he wasn't prolific in front of goal until his 2nd full season when Rodgers came in. He was always a top player though, Nunez is just so raw as a footballer, not just a finisher.
Depends on what you mean by 'come good' I guess. Suarez certainly was excellent from the outset but he did have that 'not a finisher' label. I distinctly recall people clamouring for Huntelaar or thinking Carroll would be the finisher in a partnership lol. Nunez on the other hand often seems incapable of doing basic things like moving with the ball or placing the ball from 6 yards out. If coming good is reducing the variability in performances then I think we've definitely seen this albeit starting from a higher base. For example, Mane's first season to his third was such a step up it was unbelievable. As was Firmino's improvement. The concern with Nunez is that he's consistently putting in performances that are just objectively awful, which I don't think we've seen resolved before. And when it's going wrong for him he rarely resolves it in the game.
I want him to succeed, he has all the physical attributes to be a great player. He just seems to lack something mentally.