Wind Neftis could probably replace Hastur if you can make up for the difference in -def elsewhere (for example, through Hraesvelgr on your friends list or you opt for that def debuff from Gawain as your ex skill). As long as you can brdige that -def gap, the main difference is that wind Neftis has that maximal damage against stunned enemy buff versus a party assault buff.
Otherwise, given that core team, just stand pat.