I agree, they're not better than mine.

Still, the technique is interesting. I think you first have to have stacking in mind when designing the rocks, however, which mine did not take into consideration and to have a few very generic rocks that kind of interlock a bit with only a bit of scaling.
I have to be honest, though, I don't care for that cave at all. I think, for Terragen, you'd be better off using displaceables, or a displacement map to get a basic cliff / cave entrance, and then import some sculpted rocks to pretty up the entrance, and maybe try stacking with those. But seeing those rasterized textures fail at that scale reminds me of the N64 era.
Of course, I could always model a cave entrance and release that...

However, then you lose the ability to custom build it. As with anything, it seems, it always come down to substituting one benefit versus one drawback for another.