I'm really struggling with constraints.
Nope, you are struggling with constraining a 3d sketch.
Stick to 2d sketches until you can't.
Where is the wing? A wing tip should transition off the wing. Can use it for the dummy bodies I needed.

Usually build the profiles or rails first, so the preceding 2d data can be projected into the current sketch.
I extruded your wingtip band back through the wing rib and trimmed it off.
Traced the canvas with a minimum spline for top and bottom rails. (Yours has way too many spline points.)
Then a sketch plane on each of your upright lines.
Sketch on each plane, project the top, bottom rail point, and the plate, gives you this data in purple.
Snap a spline to the 3 points. Make the spline handles horizontal or vertical as required and adjust the curve to suit. Same for next 2 planes.
Extrude the top rib curve into the wing direction. Extrude a second dummy body for bottom curve. Hide rib sketch.
Create a 3d sketch. Project > Include 3d geometry - select the Leading edge point, each spline point for the tip outline, through to the trailing edge. You get 5 purple points.
Draw a Spline from front, to back snap to the 5 purple points. Top view and make the LE spline handle horizontal/vertical depending on how you look at it.
Adjust the trailing edge handle, until the curve looks good for you.

Before the Loft preparation should look like this, (all black sketch points).
Create Surface Loft.
Select the LE point, profiles from the 3 sketches (in order) and the trailing edge point for Profiles.
Select the top body edge, tip band 3d spline and the bottom body edge, as Rails. Edit the rails to be tangent.
Remove the 3 dummy bodies, and Boundary fill if you want a solid or Thicken for skinned solid.
Step my Timeline, happy to answer questions.

Might help....