This [Tenet Diplos] build utilizes a magnetic or radiation (whichever you prefer) progenitor. Note that Magnetic allows you to be lazy and not have to swap mods out for Corpus, while Radiation allows for swapping mods into magnetic + toxin vs Corpus and keeping the Radiation damage for use against their robotics (Moas, Ospreys etc.) The idea behind the combined element progenitor is to maximize your [Galvanized Shot] damage bonus.

It uses a standard Viral + Heat setup while focusing on maximized critical damage, foregoing status chance. Don't forget that if you swap out the elemental mods for their status + element variants, you can get around 50% status chance, losing a bunch of damage in the process. This option, though, will require less Forma.

Secondary Merciless is great, but Secondary Dexterity is a completely viable option if you're going for extra combo duration.
Realistically, you don't need an Exilus mod on the [Tenet Diplos], but [Lethal Momentum], [Reflex Draw], [Steady Hands] are all useful in their own way. Suppress and Spry Sights might be interesting options as well.
If you have a riven mod, I'd advise rolling for +cc +cd +toxin/cold with a harmless negative like -zoom and slotting it instead of [Pathogen Rounds] or [Deep Freeze].
Just make sure you remember shooting before aiming at an enemy to avoid the homing mechanic.

Hope this helps, Tenno.