Banish III is not PLD usable, its WHM only(not to mention the HORRID cast time and mp cost to begin with..), and PLD hsa B- Divine, WHM holds the best Divine with A-.
PLDs usually dont outlast NIN RDM or MNK in ballista in general, this will help them alot, however i dont think its enough to push them to that degree yet...Cures with 9 people hitting you usually dont pull out and any WS from an evenly matched player(everyone is EM after all) is usually enough to take you down to a sliver of life if you are lucky in ballista. Our only real dmg is 300TP Spirits Within or a good Vorpal/Savage Blade.