Radiation as progenitor to prep for [Galvanized Savvy]. Don't pick Heat as you'll always have [Blaze] in almost any other build.

Radiation + Cold is good against alloy armor, try steel path's acolytes.
Acolytes have ferrite armor, which is weak to corrosive. Stalker has alloy armor.

For viral + slash build, swap electricity with toxin, [Blaze] with [Hunter Munitions], and [Primed Tactical Pump] with [Chilling Reload].

For corrosive + heat build, swap cold with toxin, and [Primed Tactical Pump] with [Galvanized Savvy]. (904k Burst)

Update (21/09/21): Fatal Acceleration --> Narrow Barrel, Primary Merciless --> Primary Deadhead
You'll almost never use the alternate fire from more than 15m from the target anyway, the pellets will likely scatter out of your aiming reticle.
The reduced spread is quite noticeable for both normal fire mode and alternate fire mode, making it more usable.
Primary Deadhead is easier to maintain, especially during the kuva lich final confrontation, where you're not likely to encounter a lot of enemies.