Definitions:
If Roshar gets to give Ishar the Dawnshard, Ishar singlehandedly wins - Dawnpowered Surgebinding was sufficient to devastate the planet of Ashyn.
Otherwise, Scadrial has a number of options to achieve victory:
1. Spike A-Gold and F-Gold into someone with the desired power. Hemalurgically spike the desired power out of them. They can survive this and heal, via Gold compounding, allowing you to create an arbitrarily large number of spikes of any Allomantic or Feruchemical power. Create an arbitrarily large number of soldiers who have devasting powers such as A-Steel, F-Steel, A-Gold, F-Gold, A-Pewter, F-Pewter, A-Chromium, etc.
Scadrial can create an army that can break the sound barrier, survive fatal wounds, crumple steel with their bare hands, dissipate their opponents' investiture, and more.
2. Create an army as before, but do so by producing more Bands of Mourning.
3. Even without these hypothetical armies of devastation, Scadrial can field at least 3 Fullborn (or equivalents thereof): Marsh, Kelsier, and whoever is wielding the Bands of Mourning.
4. Provide the aforementioned forces with a healthy supply of Atium, allowing them to peer into the future, and easily bypass attacks that would otherwise kill them.
A fullborn should be capable of killing any Radiant except possibly Bondsmiths. The Bondsmith matchup depends whether a Bondsmith can use Connection shenanigans to defeat a Fullborn before being killed at the speed of sound.
Jasnah Kholin performed a number of impressive feats at the Battle of Thaylen City. This is notable because she appeared to be able to Soulcast things that she could not touch and which were not adjacent to her. I have compiled a list of what she was capable of doing. However, it is important to note that Dalinar's subsequent Perpendicularities have not demonstrated the same potency as the one he created after recently swearing his Third Ideal. Furthermore, compounding things like Identity, Investiture as well as Copperclouds, A-Chromium, A-Aluminum would probably protect the Scadrians from directly being soulcasted, and supersonic speed, strength, etc. should be enough to escape or break through attempts to trap them. Finally, it's not as though Bondsmiths can just swear more Oaths upon demand. If we charitably suppose that there are three Bondsmiths at the start of this conflict, all of whom are ready to swear their Third, Fourth, and Fifth ideals, that would only be six instances in which an Oath-Boosted Perpendicularity could be created. Couldn't the Scadrians simply retreat on those occasions? They would suffer loses but this should not be enough to defeat them wholesale.
Jasnah's Feats at the Battle of Thaylen City:
Words of Brandon that support various assertions I make during the course of this post:
Invested Spike Factory:
A-Chromium Prevents Shardblade Summoning: (and probably prevents Shardplate as well)
Copper:
A-Copper is shown to interfere with another Invested Art, in several ways. Can this be extrapolated to suppose that it would interfere with attempts to use Surges on or very close to a Smoker? I suspect the answer is yes, although I acknowledge it as an uncertainty.
A-Copper Blocks Lifesense:
A-Copper Interferes With Awakening Colors: