All of the gear you mention has some lore surrounding it.

Each AF has a story that you learn during job quests. The myth gear is AF replica's that Rowena has acquired to dole out to adventures for a price. The soldiery gear is old Gerolt gear that Rowena has been stowing away to sell. The upgraded stuff is restored by Gerolt's apprentice.

Form a lore perspective, only the original AF makes sense to be involved in some sort of upgrade, but not for any of the gear that currently exists, without altering the lore surrounding those pieces.