Well, would you look at that! doing the complete import 'babylonjs-loaders'; seems to do the trick. still getting a 0 vertices count on the new scene, but definitely gives me more to play with and now completes loading without error. Might be worth a mention in the docs somewhere as webpack setups are getting more and more common these days; I forget where I even saw the initial setup but would be glad to recommend a note to be added if I run across it again.
Hopefully that clears it for anyone else encountering this stumbling block. Thanks so much for your quick reply, and for the engine itself!