When adding parts to an upgrade then the upgraded item gets exp.
When adding parts to an transformation, the part becomes it’s next stage without gaining experience from the materials required.
Now when you use the materials needed to transform an part to it’s next stage the parts added should also be materials for exp also.
Transformations originally doesn’t enhance exp when using materials to make it.
The improved version would be adding experience to the part when transforming it with the item’s natural exp.