So from what I can find, you're right in that it's not 100% goo, but it's not really "coordinated small steps either". It's a messy fluid process that all sort of happens at once. When caterpillars are inside their chrysalises, they first digest themselves by releasing an enzyme. But this enzyme doesn't break down everything. Some organs are completely dissolved and completely new ones are grown from the goo, but most only partially, and are moved around remodeled into their butterfly counterparts. As for the entirely new parts, like wings, they've actually been inside the caterpillar since before the cocoon as these tiny clumps of cells call imaginal discs, and it's only during metamorphosis that they begin to develop into their full size organ. It's really cool, and you should read more about it. I'm no expert, so I'm sure I explained it badly, but here's some good links.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6711294/

https://downloads.hindawi.com/journals/psyche/1897/062863.pdf