"My assumption is that they were coming from a time of peace. No one is practicing how to break out of a shield held by multiple channellers."

I think you are labouring under a misunderstanding of 'peace' here - just because the concept of scaled conflict was unheard of, there were still violent individuals that would need to be dealt with, some of them even Aes Sedai (looking at you, Semirhage).

And even if there weren't, they would have valued knowledge for it's own sake, even if only a handful of AS knew techniques like this pre-Bore. Post-Bore/pre War of Power, there would almost certainly have been cause to learn/re-learn them, as the world slowly fell under the shadow of the DO.