Most of the mission set of SF is Train, Advise, and Assist and when required, direct operations.
True, but the author mixes SOF and SF.
SF is a part of SOF as are the Rangers, SEALs, PJs, CCT and a host of others.
SF does the bulk of Train, Advise and Assist.
But that all depends on the mission. If the mission is to train a logistics system a leg major from Big Army might get tagged.