Best designs are produced by small, tightly-knot, often one-person design teams. Examples: Unix, Clojure, SQLite, Boeing-747, Westminster Palace in London.
Sometimes a small team with a cohesive vision keeps on attracting like-minded people or matching ideas, and the project grows with contributions from a large number of people. The key part of every such success is the vetting process. Examples: Python, Ruby, FreeBSD and OpenBSD.
Worst designs with most glaring, painful, expensive, even tragic shortcomings are produced by large committees of very important people from huge, very (self-)important companies, agencies, departments, etc. Each of them has an axe to grind or, worse, a pet peeve. Examples: PL/I, Algol-68, the Space Shuttle (killed two crews because the escape system was removed from the quite sane initial design); to a lesser degree, it's also HTML, CSS, and, well, C++ to a large degree :( The disease has a name [1].
Sometimes a relatively small and cohesive team in a large honking corporation produces a nice, cohesive design, like this happened to Typescript, certain better parts of CSS, and some of the better parts of C++. This may sometimes make a false impression that "design by committee" sometimes works.