If the DXF was imported at massive scale, then reduced, you might have a LOT of nodes in the design, and that could be part of it.
DXF files that contain splines store them in a format that isn’t compatible with how LightBurn (or other artistic software) represents them, so they’re converted to line segments within a distance tolerance of the original shape. If you import the design at 100x the actual intended scale and then scale it down, that “distance from the true shape” part of the code is being run at the enlarged scale, so you’d have about 100x more nodes that you should.
In the settings, you can set the DXF import units in the ‘File’ tab, and that will do the scaling before that spline evaluation happens.
You can also use Edit > Optimize Selected Shapes and convert the splines into arcs that are within a specific tolerance of the source: