If your single track trails are rocky and rooty the fat bike will beat you up.
Modern more or less means thru axles and 150mm front hub spacing and 190/197 rear hub spacing and 1x drivetrain. Some fat bikes have also gone to 68 degree head tube angle making them a little more "trail" friendly.
Surly is just a fad that has come and gone. They are being outgunned by other bike manufactures. I wouldn't even consider one.