Clearly, the final shape had to be approached in stages.
A wide gouge of relatively low sweep like a 5/35 to establish the contour.
If you can afford a big scorp, that's next.
Otherwise an "inshave" such as is commonly used for chair seats like everybody else.
Try to find one of them in a country garage sale.
Me? I'd go at that with an elbow adze and a D-adze that the Pacific Northwest native carving community
use for the dramatic curves on poles and feast dishes.
Then, very long shaving cuts with crooked knives, maybe a little sanding at the very end.