I'm not sure what you mean? Are you saying a 6000lbs axle can hold 9000lbs? If so, what do you have to back this up? Every trailer I've looked at has had gvwr matching the axle capacity.
This is what I mean by what I posted. An axles weight rating is exactly what its designed to carry and not fail under normal use. Here is my proof to back my statement. These are my personal trailers and what they are rated for.
53' Westwind, 3-7000# axles, 30k GVWR...
48' WW hauler, 3-5000# axles, 18k GVWR...
21' Interstate, 2-3000# axles, 7k GVWR...
18' PJ hauler, 2-5000# axles, 12k GVWR...
I don't know what trailers you looked at and seen the axles rated the same as the GVWR of the trailer but none of my personal trailers are rated in that fashion. All our equipment trailers in the stage yard are rated higher than their axle capacity too!!