I hope that the arcanist/smn has two mode of battle. One where they set the pet on auto attack and occasionally use abilities corresponding to what element it is. The other being the player channels and looses complete control over themselves to gain direct control of their of their pet with added power buffs.

Why the buff in pet power when in direct control? Obvious reason is the lost in control of the main character.

Why would you want direct control of a pet? on how the pet's abilities work, I remember seeing "Tank" on the arcanist slide image. Would you like tanking to be left up to game AI? Would you like to be able to optimize pet DPS output over the lost of control of the main character and any abilities they may have had.
Say for instance you set up cure/stone/raise on SMN (This is me assuming one of SMN's usable abilities is in CNJ) But you want to go completely into your fire...dog...thing... or w/e and gain full advantage of all their abilities (Which I suspect will be large enough to warrant staying in that trance mode ie the ability to combo and what not) while at the same time loosing cure, raise, and stone.

But in all I rather just see some gameplay on arcanist. ; ;