Throw a quick contagion during down-time to clear enemies and stack up the Dexterity Arcane; it's the easiest/quickest weapon Arcane to stack up. The stacks allow you to one-shot pylons even without a Riven.

Riven stat priority: MS = CD ~> Dmg = Elemental > CC
Riven replaces mod with same stats, in reverse priority; If riven has Elemental damage then replace the Elemental mod of the same type.

[Saryn] Elemental Coverage:
Saryn(all weapons): {Corrosive+Toxin}
Zenith: {IPS}+Corrosive+Cold
Kuva Nukor: {Radiation+Magnetic}+Viral+Heat
Contagion Zaw: {IPS+Viral+Blast}+Gas+Electric
{} = innate damage types.
Viral is used on KNukor because the Contagion explosion(the part that is Viral) only hits PT if aimed at a specific spot to the left underneath it, making that less reliable.
All combined elementals are covered by KNukor+Zaw, so Zenith can cover Corrosive, allowing you to skip casting Spores(Corrosive buff) during the first shield-phase, saving 1-2seconds(slow "cast") when speedrunning.

[Volt] Elemental Coverage:
Volt(all weapons): {Electric}
[Zenith]: {IPS}+Gas+Cold
[Kuva Nukor]: {Radiation+Magnetic}+Corrosive+Heat
Contagion Zaw: {IPS+Viral+Blast}+Magnetic+Toxin
As I see it, there are two main ways to go with [Volt]. Either you go for the "ass meta", where contagion throws are aimed at a specific spot on PT so that they deal the Viral damage, and use the types listed above, or you use the same builds as Saryn does, but put Toxin on your archgun.

For runs without Volt/[Saryn]:
Same builds as [Saryn].
All 6 combined damage types are covered, but there's simply no way of covering all 4 base types with 3 weapons, because even if you subsume [Volt]'s Shock to buff, the Electric will just combine into other damage types. Saryn's 3 and Volt's shields are unique in that their Toxin/Electric damage doesn't combine into other types. It's more helpful to subsume Smite, to cover Radiation on all weapons.
Also note that [Chroma] players can replace their +Damage mods with something else for more damage.

PT builds:
Saryn/Volt/Chroma/Wisp
Zenith
Kuva Nukor
Contagion Zaw
Mausolon
Smeeta(for credits)/Adarza(for speedruns)