In my head (suposing I can get the relics I want), there are more good chars than vacancy in my ideal party:
Suport role: Fran (Full Break SSB, that aside being stronger than Full Break ability, it last longer + att/mag down SB, that is excelent mitigation tool) with wrath and another breakdown;
Healer: Yshtola (wall)
DD role: too many options:
Bartz (Trueblade of legend + defense boost)
Locke (Valiant Strike, Thiefs Revenge - massive overhits that will be excelent when stacking various defense debuff)
Cloud (Fenrir Overdrive)
Auron (Banishing Blade - another defense down debuff to bring mob defense to its lowest possible)
Tyro (yeah)
Probably my default RW will be Quina mighty guard.
Its a shame we just can go with 5 char.