I personally had a robot, and I do not see a reason to have full on defense because the pet acts like its in "do nothing" mode. It tanks drill bots just the same as it does when I have it in attack mode.
Perhaps have a booster mode, but instead of boosting dexterity or critical hit chance (because I [and pretty much everyone above level 200] have 300 dexterity), boost defense or health or mp/mp restoration?
Or anything else to boost? (No power/magic/artillery/range because that would defeat the purposes of spirit orbs)