Verbatim self-plagiarism in introductory sections
There seems to be no risk of getting credit twice for the same work here, as the papers are fundamentally different. It is possible that more modifications to these paragraphs would make them better suited for their role in the new paper, in which case suggesting that the authors do so is appropriate for the referee. However, rewriting the paragraphs just for the sake of it seems like a pointless endeavour. As a referee, you should not suggest that the authors waste their time on this.