Except there are large projects using Mercurial without issue. See Facebook for example. If you want to look at open source projects, all of Mozilla uses mercurial[0] with just the standard hg-web server. And it's size is comparable (same order of magnitude) as the linux kernel)[1].

If you want to make such claims, I'd love to see data backing it up.

[0] https://hg.mozilla.org/

[1] https://www.openhub.net/p/compare?project_0=Mozilla+Firefox&...