Pruning pages

My client and I are having a conversation. He wants to prune a lot of his blog pages. In itself a good idea to merge almost the same content, we agree.

However, there are a number of pages that are very similar, but highlight a subject slightly differently. As a result, not 1 but 2 pages are shown in the searches for a certain position. He also wants to merge these.

For the low positions in the SERP, I agree with him. However, he also wants this for the pages that together occupy positions two in the search results. And here we differ.

My idea is that a duplicate listing should be kept at position 2, and brought to position 1 with some support from backlinks. He thinks position 1 will move faster with the merging of both.

I am very curious about your opinion.