The Churchill line is about democracy, but the adapted version is a common variation. It works as a standalone maxim without need of attribution to some famous person.
Got any evidence for that?
Forbes, 2019: https://www.forbes.com/sites/yuwahedrickwong/2019/04/19/econ...
NPR, 2009: https://www.npr.org/2009/10/26/114163098/a-spoonful-of-socia...
LSE Economics Society essay question, 2018: https://www.tutor2u.net/economics/blog/lse-economics-society...
I also clicked through ten pages of Google search results for "capitalism is the worst economic system, except for all the others", each of which showed the literal quotes in the preview excerpts, at which point I became too bored to continue.