I'll keep this as short as possible.
Magnetic damage is not awful, not good, but not awful. Its Disruption Proc, however, is. The new arcanes are nice, but they do not fix the problem Disruption has.
It is a proc that only has a single faction it is useful agaisnt, and a handful of other enemies, but it is surpassed by the primary elemental proc from Toxin.
The proc is similar to Viral, but Viral has a use everywhere (bar the Murmur). This is why despite not being the best choice in every scenario Viral is still used everywhere, it is about ease of use.
Magnetic has none of that, it is niche and withing its niche it is surpassed.
How to fix it:
Give Magnetic procs (Disruption) the effect of Void procs (Bullet Attractor).
Make it stackable, make the bullet attraction grow with stacks, maybe only 1 meter atraction with a single stack and then growing by 0.5 meters per stack to a maximun of 5 (3.5 Meters) or whatever ends up most balanced. Keep the disruption part of stopping shield regenerations, it is good, but the extra damage to shields could actually see the bin, the type effectiveness covers it enough.
Why:
Bullet Attractor is a good proc, not good enough as to put Xata whisper on all warframes as a helmith ability. There are some better choices, but i definitely have it in some frames. But as a magnetic proc, not only would it make magnetic damage more desirable, it would see some niches with low accuracy high status weapons, but the niche would be weapon specific instead of faction specific, giving the ease of use it deserves.
Possible criticism: Bullet Attractor on Magnetic damage would overshadow Mags Magnetize.
Xakus Xata Whisper already gives void procs to every single weapon, I don't see it overshadowing Mag. It is thematic, as mag is a Magnetic frame, it is a nice tie-in between themes and mechanics.
What about Void procs:
I never knew why Void has Bullet Attractor as a proc, it doesn't make sense in the world building, and makes very little sense mechanically too. The operator abilities dont really mesh well with it as a mechanic, it is cluncky to use it as a primer for warframe weapons, and nothing in Xakus arsenal suggests it should be the case.
I propose another proc for Void damage that is thematic with what we see in the game, being toxic to living beings and to the sentience.
New Void proc: Discordance, the anti-adaptation.
Decreases the Type resistance of the targets primary Health type by 10% increasing by 5% per stack to a maximum of 8 stacks, (50%). Effectively making them 50% more prone to damage from all sources.
To explain the way that I see it working, I'll use 2 examples: If you are attacking a Heavy gunner vs a Butcher.
There could possibly be a less cluncky way of doing this, but this one is the most interesting way to me.
Why:
This is mechanically a better Operator primer for Warframe weapons, while also working better with the Operators own kit. it does power up Xatas Whisper, but it is still not close to what some other Helminth Abilities can do (it also already has diminished effect when helminthed). Either way it powers up any damage type you are using.
Thematically it makes more sense with how the void behaves, removing resistances from the sentients, scrambling Profit-Takers shield vulnerability, and even makes more sense with The Indiference, who targets your weakspots, emotions, manipulates your memories, proding at the wound.
Possible criticism: Isn't this Viral 2.0?
It is not. The source of Void damage is much different and restricted than Viral's, only Operators and Xata Whisper can do void damage as of now. It should remain restrictive for the forseable future, so I do not see them in the same vein. It also works with all enemies similarly but to a lesser degree.