Ground PVP is class specific, GSF is the same for all characters. No reason why it shouldn't be legacy wide or at least faction wide. Once again, glorious engine makes a stand.
Why unlocks like CM ships are not in Collections or legacy perks, this is BW decision and not very good IMO. They want people to play GSF from different characters, because in long term it could bring them more money from CC customization and other related stuff. But character locked ships for 1800CC? People will never move from main to play GSF.