The Arcanist cross class skills (past physick, which is a useful heal for soloing/partying), are for support to lower incoming damage.

Those skills are nice for endgame, but completely unnecessary while leveling/dungeon running.

So its up to you. Keep in mind, you also get 50% increased exp after you get one class to 50. So i would suggest getting arcanist to 6 (or was it 2?) for the heal, then maxing your THM before going back and getting arcanist skills.