If you were designing the very first bike for riding off road on rocky, rooty, trails and wanted the best compromise of traction, comfort and speed I think what you'd design would be a FS bike. Hardtails are, I think, something of a a legacy from MTB's infancy.
However anyone can ride what they want to, the choice is theirs.
FS saves my back from a beating and after riding hardtails for years I wouldn't go back. Having said all that my FS is a mere 4 incher and pumped up hard (oooh er missus) it's also a single pivot, my bearings are almost 10 years old and get used several times a week so I don't see a downside to FS.