(a) no evidence of better performance. Lua/Nginx is very fast too.
(b) Its just a proxy, while Lua/Nginx/openresty is much more of a full web development environment. You can use it as a proxy, but it is not the main use case.
(c) I don't think Traffic Server has more capabilities, as far as I can see, I think it has fewer as it is much more focus on being a proxy product, while Nginx is a full web server.
