They all soulcasted in a controlled environment, and focused for several seconds before succsesfully soulcasting.
The vast majority of your electrum shadows freezing in place is a very good indicator to dodge, and with steelpushes, a Mistborn will be able to get out of the way unless the Lightweaver has perpendicularity levels of Stormlight.
Yeah, but we've never seen a Lightweaver combat soulcast. In fact, the only person we've ever seen do that, unless I'm mistaken, is Jasnah.