It's not that BDJ/Java is brain-dead. Far from it, it is a functional virtual machine. It is however heavyweight for relatively simple stuff like overlays and menuing systems.
This same debate goes on and on in the computing world. On the client side, Soap/Ajax-based apps vs Java, on the server-side, PHP apps vs Java, in next generation media, HDi vs BD-J.
Personally I would say both can get the job done. Which platform is "better" really depends on your target application and the "support" that is given through libraries for common tasks.
I do see though that there a lot more HTML/Scripting-type programmers out there than there are Java programmers. I think anybody with C/C++ programming experience can pick up new programming languages pretty easily, so for them, I don't think the platforms are really a barrier to entry. However I also do think that for people that are more media-oriented with less programming experiencing, scripting is easier to pick up, especially if someone like Microsoft has built (or helped develop) a lot of existing libraries and common functions for you along with authoring tools.
If I had to port some larger complex app that was written in C, I would probably choose BD-J also. However if I needed to do some menus for the disc with some PiP commentary, I would probably use HDi. However that isn't really a choice here, if the disc is for BluRay, one must use BD-J and for HD-DVD, one must use HDi.
As I mentioned earlier, both can get the job done for the common tasks used in next-gen media, however I think the BD-J folks are finding lots of primitives, libraries, and authoring tools are either not mature or not written yet so they end up implementing much themselves. This will change over time of course, but there will probably always be the debate of whether HDi or BD-J is "better" and to some extent I think it will just depend on your background and what you are more used to using, scripting or Java. I guess it is just par for the course with this "format war", to choose programming methods that add further to the polarization.