Do external links with nofollow hurt SEO or leak link juice?

I love to use the example of Wikipedia. As you may know, Wikipedia adds a nofollow to every single external URLs on every Wikipedia page so that at the end of every page, there are tons of nofollowed external URLs. Below you can see a screenshot. All the nofollow external links are surrounded by a red box.

If I google “Vint Cerf”, the first result is from Wikipedia. The third one is from…google. The first wikipedia page has numerous external pages with nofollow. On the other the google page about Vint Cerf has no “nofollow” at all and no external links. This means that the page with numerous external pages and nofollow attributes can outrank another page with no external links.

Then, we still don’t know if adding external links lower the link juice of a web page. If you have 10 internal links on a page, we know that every link leaks the equivalent of 1. Then, if you have 10 external links on the very same page, we don’t know if it divides the link juice sent by internal links by two “0,5” or if the link juice for external links is added to the page.