I will spoiler this since you did, but do you guys want to continue using spoiler text with it being nearly a month since the release? Don't care either way, just figured I would raise the question.
A few things at play here. Shallan kills Chana around the same time Gavilar is killed. Based on when Taln reappears at the end of TWoK, she lasts a few years on Braize before giving in. Odium could send spren over at that point due to the oathpact being weakened, but couldn't actually return the fused until a herald broke.
Now there was a few weeks/months between that happening and the everstorm, so I guess he technically could have started bringing them back the old way (like he does with El at the end of RoW). But I assume the reasoning is that the Everstorm allows him to completely circumvent the Oathpact stipulations, and at that point had spent years pulling strings to make it happen. So I think ultimately it was about not showing his cards until it was too late. Also, I think the everstorm probably was vital to restoring connection to the rest of the slave form parshmen after Mishram was imprisoned. But I might be missing something there, as it's not completely explicit imo.
A few things at play here. Shallan kills Chana around the same time Gavilar is killed. Based on when Taln reappears at the end of TWoK, she lasts a few years on Braize before giving in. Odium could send spren over at that point due to the oathpact being weakened, but couldn't actually return the fused until a herald broke.
Now there was a few weeks/months between that happening and the everstorm, so I guess he technically could have started bringing them back the old way (like he does with El at the end of RoW). But I assume the reasoning is that the Everstorm allows him to completely circumvent the Oathpact stipulations, and at that point had spent years pulling strings to make it happen. So I think ultimately it was about not showing his cards until it was too late. Also, I think the everstorm probably was vital to restoring connection to the rest of the slave form parshmen after Mishram was imprisoned. But I might be missing something there, as it's not completely explicit imo.