Gas and Magnetic damage is useless because their DAMAGE PROFILE and STATUS PROC serves the exact SAME function. Every other elements are multi-purpose! Please give Magnetic/Gas (and Blast) a new effect. :
Warframe | How Damage Works #3: Combined Elemental Damage - YouTube
All Warframe Damage Types, Explained - Pro Game Guides
Warframe damage types - what enemies are weak against | Rock Paper Shotgun