Get selective folders of Time Machine backup on a new iMac
Open finder and navigate to the folder on the Time Machine volume and drag it on to your desktop.

Time Machine places each backup in it's own folder so you can easily get to the one folder you want to restore and do it by hand. You can use the Time Machine interface to restore that folder as well, but Finder is more direct. You are correct so skip migration assistant as it's not the right tool for your job.