This is an interesting breakdown, but here's my analysis:

Let's say that ~100% of Etsy.com views are through Safari. Of those, 100% have iCloud+.

Let's say they did this and 0% of people visit the site through chrome.

That's 100% less revenue for them. Pretty amazing that this one feature could completely kill Etsy's revenue stream.

(For what it's worth, I agree with you that Etsy is not going to tell Safari users to pound sand, but your arbitrary numbers don't make an actual point unless they're based in facts and figures.)