Yes. While how Fusion works is interesting, it adds risk of data loss that I avoid. And using it with external drives would be kind of crazy as they add additional risks.
Yep. I also agree that as SSD prices fall Fusion will become less relevant.
When I bought my iMac at the end of 2014 I paid extra for a 500GB SSD, and I bought a Drobo for bulk storage. All my apps, mail, whatever, fits nicely on the SSD, and I have my iTunes library, my Photos library, Plex library, etc, on the Drobo. The system is fast for the things I need it to be fast for, and the Drobo is plenty fast enough for iTunes and Plex. YMMV.
There were people who only got a 128GB SSD, then had to resort to symlinks and other hacks to get the bulk of their data stored somewhere else. I thought that this was “penny wise/pound foolish”.