... from Heda's file redrawn just for fun.
(A little bit bigger !! Because I had to do with the CRV-vehicle Bodyflaps some 25 years ago).
https://en.wikipedia.org/wiki/Crew_Return_Vehicle

... "nearly" no problem in PartWB ???

... I can confirm this behaviour in another application. After/when using the Convert to BSpline tool the Constrain bar gets sometimes incomplete, like shown above. OS: Windows 10 build 19045 Word size of FreeCAD: 64-bit Version: 0.22.0dev.35594 (Git) Build type: Release Branch: main Hash: 49e7bba9c...

... Finger pipe => conic by Helix and oval by Link scaling:
The end rings could be tilted by little effort.
And the sweep profile should also be tilted to Helix cone angle.

... a primitive trial, still without edge fillets.
(and one round too much)

... bottle modeling reduced to the basic.
Transition from bottom to neck could be done with another Facebinder Loft sequence (Bottle_3 and Bottle_4).
The bottle quarters are copied and positioned by Link tool.

... a real task:

... just another trial with 3D-Offset blades.
Where is the magnet for the Hall_sensor?

... another trial with Loft (and/or Gordon) => not parametric, but Solid:
And a Sweep solution.

... a first trial with profiles for a Loft: