Did you try to manually create some of your 10K products, export them and use the export.xml as a template?
I did that, and I’ve realized that there is a column called “attribute_set” where I can write down the name of my attribute. It will be imported and recognized.
I didn’t find to do something else though. Don’t know if you also have Configurable products to link to simple product in your file? I had to do that but didn’t manage to automatically link them to each other. (had to do it manually).
Let me know if you manage to do it.