FRWSTARx books into A booking class. On some routes easily available and on others impossible (eg SQ A380 has zero A booking class ever).

Many *A airlines have no first class - these would book into business class instead.

Some *A first class is excellent (eg SQ longhaul product), some average (eg TG) and others terrible (eg UA).

Depending on your routing and where the RTW is purchased from you may or may not get good value by buying F instead of C.