devtrackers.gg
Mod types are roughly color-coded. Red is Damage, pink is Multishot, orange is Crit, and green is Elemental or IPS. Variant mods are counted the same (Amalgam Serration → Serration), and lower-tier version are rounded up (Heated Charge → Primed Heated Charge).
Rifle Builds
Only 27 different mods are present in the top 80 Rifle builds on overframe.gg.
Split Chamber is present on every single build. Serration is present on all but one, a build for Eidolon hunting with Chroma.
9/10 builds are Crit-focused, and Heavy Caliber and Vigilante Armaments are present on 2/3rds of all builds. 1/3rd of builds use Hunter Munitions. 1/8th use Hammer Shot.
Every single build uses at least one 90% or 60/60 Elemental mod, 2.25 of them on average.
Damage, Multishot, and Crit > Elemental > Other
Secondary Builds
Only 25 different mods are present in the top 99 Secondary builds on overframe.gg.
Hornet Strike and Barrel Diffusion are present on every single build, with Lethal Torrent existing on 9/10.
7/10 builds are Crit-focused, with 1/3rd using Magnum Force. 1/5th use Augur Pact.
All but one build uses 90% or 60/60 Elemental mods, 2.8 of them on average.
Damage and Multishot > Crit > Elemental > Other
Shotgun Builds
Only 22 different mods are present in the top 21 Shotgun builds on overframe.gg.
Primed Point Blank and Hell's Chamber are present on every single build. Vigilante Armaments is present on 2/3rds.
Only 1/5th of all builds use Crit mods.
Every single build uses at least one 90% or 60/60 Elemental mod, 3 of them on average.
Damage and Multishot > Elemental > Crit > Other
What all of this means is what we all already know: modding guns in Warframe is boring. You do the same build on every weapon you get every time. This is something that's been plaguing Warframe for a long time, and it's something that really needs to be addressed.