I think I've found the culprit, after a good 6 hours brainstorming. Turns out, the Reset XForm modifier on the NWMax window worked differently than gmax's own one, in that NWMax collapses the modifier tree after applying the XForm modifier.
Oh, and thanks for the tip. I usually mis-prioritize the steps in the export process. I'll make sure I reset before linking.
I'm more of a '3d fabricator' than a '3d modeller', meaning I prefer to construct things from reference, blueprints or schematics rather than to design stuff of my own.