I had a very similar concern; see here: https://www.dropboxforum.com/t5/Dropbox-Paper/Dropbox-Paper-Public-link-WITHOUT-commenting-and-sharing/idi-p/210661
Unlike you, I didn't get any response from Dropbox, but hope this issue is getting some traction. I completely agree, these pop-ups and the huge bottom banner are very annyoing. Notion (what we're using now) and Box allow for simple page sharing without aggressively pushing the viewers to sign up for an account.
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