only in the simulator. Sabre/Rapier/Ferret are part of the system security forces and are no longer stationed on fleet carriers by the end of the war.
I don't think this is accurate. If anything, these designs are all (or mostly - the Ferret is known to be older) newer than the fighters flying off of the Victory in Wing Commander 3. All three of these designs are still front line units at the end of Fleet Action (late 2668/early 2669), mere months before Wing Commander III. That same story makes it clear that things like the Sabre-D upgrades are part of the backbone of the fleet's future plans... and Rapier II variants, at least, are still flying for the Confederation through the Nephilim War.