'....would start side to side oscillations until it dove to the ground...'
I attach 2 photos - I guess, Your wings are missing 'stabilizers' where rods are crossing, to avoid warp of the wings. I also can not recognize kind of 'angle of incedence' (tail-lift for example).
Here are 2 videos with eagles having stabilizations as named:
If You would try a 1000mA Lipo (instead the 2200), You could save a lot of weight, and Your bird would perform better. Saving weight is the most important factor, when converting kites to Vector Kites.
'.....I am still not convinced that vectoring is an improvement on moveable surfaces....'
Vectoring as a new concept. Vectoring allows, to bring flying objects of many kind easyly without control surfaces
into the air (as kites are, but not only kites).
Give it some more tries, Joel, especially with Deltas/Deltaboxes, Boxes, Canards, Monowings (single, double, triple), X-Wings...
There is a lot more to discover, and, to experience ...