I meant the Giroud example more but both examples work I suppose.
Assuming an attacker is just there to score goals is a bit narrow minded (for want of a better term, I don't mean it as an insult). Effective strikers come in all different forms. Some are pure goalscorers, some hold up the ball well and bring others into play, some are a pain to play against etc.
Calvert Lewin is nowhere near the finished article, I think that's fair to say, but he does have his uses as well. I would be more concerned if he was missing chances all the time but he isn't really, he isn't getting chances to convert, that will be a combination of youth and the fact that he has been asked to play pretty much all over the final third and not just centrally.
Besides we had one of the best goalscorers around and we came mid table with him for three seasons. Its not the be all and end all.