I have a file that was constructed in Fusion 360 and exported to DXF:

When I import it into T2Laser, the curves are converted to flats:

This is clearly a version/format/spline/polyline type of problem. The DXF import plugin for irfanview also shows flats:

But QCAD shows curves:

Fusion 360 doesn't have options for DXF exports. I've tried using Illustrator and QCAD to change the version to R15 (and almost all others,) but the resulting files still have no curves in irfan or T2Laser.
Any suggestions about how to overcome this?