I’m going to add my two pennys here and from my experience with the Package Builder with 2020 when trying to create a livery pack, it required a MSFS ready model file which I do not always have. Building outside of the sim allows for rapid prototyping and like OP preparing externally and using the copy function is a core part of the workflow.
A lot of my work focuses on default aircraft and giving them some love. Has this been corrected in 2024 so there is no longer a requirement for a non-mastered GLTF? (see previous time I have asked about this issue - Livery Textures not processing in Package Builder)
Happy to switch to dedicated tools, but the resources have to be available and functional.