Why?
Smite in it’s current form is far too readily available to offer meaningful impact outside of completely removing core gameplay mechanics and as a consequence even limits other players from being able to trigger their own interaction focused Talents like Second Wind, Duellist, Reciprocity and Dance of Death for example.
One solution would be to limit how often Secondary Smite is available by giving it charges that must be available for use, similar to Assail, Shock Mine, Veteran Nades and pretty much every other Blitz in the game outside of Psyker.
In turn, Smite can be allowed to become a more versatile tool to give allies breathing room and debuff enemies through Enfeeble or Empowered Psionics.
Below I will describe the details of what this would look like, starting with the base function of Smite, the sub-Talents within Smite, then to the buffs it would recieve from Empowered Psionics.
Primary Fire
Range is increased. Single Target stun that throws human sized enemies to the floor. Ogryn type enemies get staggered on intial blast but successive hits against them offer diminishing returns. (Useful for opening Bulwark shields, stopping Crusher overheads or suppressing Reapers.)

Secondary Fire
Powerful bolt that deals 400 damage to initial target (about half of BB), then immediately chains to enemies in a wide radius. Human sized enemies affected by Chain Lightning are knocked to the ground and recieve Electrocution for 8s, that weapons with High Voltage or Enfeeble debuff (if taken by Psyker) would be able to take advantage of. (Note: Human sized enemies would begin recovery animation after being knocked down, wouldn’t be staggered for full 8s, much like Frag Nade).
Like this (minus enemies exploding and dying):

This bolt would have a brief charge up period that gives the player time to aim a precise shot at a distant target, but brief enough that the bolt can be fired in an emergency. Think charge up of Electrokinetic staff at 3 stacks of Warp Flurry. The Psyker would recieve 50% Peril on cast, and would not Overload from casting the bolt.
This bolt would be a linear projectile like Voidstrike, which would give Psykers more options to how they approach situations with many ranged enemies, as they’d be able to apply Smite from further away.
The bolt would be refunded if no enemies are hit.
Monstrosities - would be momentarily staggered if hit by the initial bolt directly: BoN would spit players out, Plague Ogryn would be knocked out of charge animation and Chaos Spawn would drop players it has grabbed. Also, they too would recieve the Electrocution status effect for 8s, opening the door to the debuff from Enfeeble and/or Empowered Psionics.
Charges: 3 Charges, 1 charge replenished every 60 sec. Plenty of charges to always have one ready for emergencies, but not enough to use recklessly.
Enfeeble - Enemies you Electrocute have their attack speed reduced by 25% and take 15% increased Weakspot damage while Electrocuted.
When taken with Charged Strike, Enfeeble would make melee combat for Smite Psykers much safer and more effective.
Charged Strike - Your Push Attacks Electrocute enemies. Electrocuting enemies increases your attack speed by 10% for 5s.
Charged Strike would now be tied to Stamina consumption so the potential increase in melee damage from the Enfeeble debuff would have consequences to defensive ability if Charged Strike is used too often.
Empowered Psionics - The intial target takes 40% increased damage from all sources during the effects of Electrocution (8s) and the AOE of Chain Lightning is increased by 50%. Ogryns affected by Chain Lightning now recieve an additional 15% Weakspot damage during the 8s of Electrocution.