I think devx is being misused in this article a bit. Obviously the tooling for java is second to none, aside from maybe the travesty that is gradle.

What they apparently mean is how "ergonomic"/"expressive" the actual syntax and type systems of those languages are. In that case c# is ahead of java by a decent margin. Luckily java is still evolving, usually by stealing many of the good ideas from other languages like kotlin. But overall those are less language and more runtime features like project looms green threads etc.

Reified generics, value types, nullable reference types, LINQ are only some of the things that would give C# an edge in DevEx today.