People want to be helpful in giving feedback on your presentation, and often when you send a draft to an experienced executive she will say to cut it down to 8 slides. She sat in far too many boring meetings where eager young managers try to pitch ideas with endless and endless pages of bullet point slides. She probably has not read the content of your slides, and just looked at the page count.
We have discussed many times that a 50 page visual presentation can be presented in the same time as an 8 page bullet point deck, but there is something else here.
A bullet point deck can easily be compressed: reduce font size and combine 2 slides into 1. With carefully designed visual slides, this approach will not work. The moment you start cutting and combining, you are back in bullet point land.
Instead of agreeing page count, agree the time you have to present the story.