In my automation framework (different from Autodesk) I have run into the same issue and my conclusion is that there is a really significant bottleneck between Powermill and an API applications.
When you have a big project you need to extract the values in bundles instead of one by one. For example if you want to initialize a list of toolpaths with its strategy types. Then there is huge difference when it's calling by print strategy to each one separately or when it is used by:
print par "$extract($folder('toolpath'),'name')"
print par "$extract($folder('toolpath'),'strategy')"
In that case only 2 calls to Powermill are performed and it is instantaneous even with projects with hundreds of entities. But the extract approach has its own pitfalls.
Personally in the past I had some free time some time ago and tried to rewrite the Autodesk API to this approach. It is publicly forked on GitHub. But it is spaghetti and maybe not so stable, because the extract commands could sometimes fail.
I am using the extract approach extensively, but in my custom framework.
