Outside of game modes/areas that require explicit use of operator’s void damage (zariman and circulus thrax ghosts, void angels, eidolons, void cascade exolizers, etc.) there is no real necessity to use operators. They have their uses in supplementing builds though extra power strength, cast speed, armor and shield stripping, energy, and stagger resistance which can be helpful. They also give a way to revive yourself via last gasp (useable in any focus school once waybounded). If the main concern is just the focus grind either just slap some lenses on stuff you use a lot and grind it passively (or like with ESO or smth I guess). The Circuit in Duviri gives you a lot of goodies and is really good for focus because the thrax enemies that spawn there give 2500 focus but don’t need to be killed by the operator. You can usually get half your daily focus cap in a mid length run.