It looks like Fusion has problems with NGONs a lot.
This is a pretty simple model, a cylinder like shape with an NGON cap.

It seems that I need to further create a planar insert geometry to stabalize the surface flow and then cap the opening.

Otherwise Fusion works quite a long time on the OBJ to TS conversion and procuses also bad geometry.
Here are the Fusion results:
NGON is filled with crazy subdivisions and turned into triangles

I would need to remove the edges to rebuild the ngon

you dont want to have to open the file and patch in a filler.

