As someone who recently came back to Java from a 5 year stint with Rails, I can safely say this is not true by any stretch of the imagination. If you stick to those tools in the Java ecosystem which meet your requirements, you can be incredibly productive.

The problem is that the Java world is full of over-engineered solutions which are really targeted at extremely large enterprise applications surrounded by a community of folks who like to menturbate about them. As a startup, you don't need to focus on those solutions. You'll not need 99% of them.

However, you can choose bit and pieces. I'm using Vaadin, JPA and Guice and finding it incredibly productive and am able to deliver functionality in far less time than it took me in Rails. I'm not using 90% of the Java EE stack, but it's available to me if/when I need it.

Rails was a great thing for the software development world. It drove convention over configuration and caused a lot of the competing technologies to pause and question why things were the way they were. But IMHO, managing the whole Rails stack (rails + coffeescript + css in our case) across a group of people became a chore. YMMV, but the statically-typed nature of Java along with the very capable technology stacks you can assemble have eased our daily jobs tremendously.