Little late to this as I'm just doing my theory building reread and I agree. I think it has something to with Cultivation and her Pruning of Dalinar. I believe Honor gave the Dawnshard to her for protection, hence her hesitation towards giving him his boon. This would also explain his strange change in behavior before his death. I think Tanavast wasn't as able to seperate the Shards intent from his own mind as well as he could when he also had the Dawnshard.
A part of me also wonders if Bondsmiths get their shardplate in their third oath, or that he may have swore another oath as well. We know that shardplate is the manifestation of lesser spren right? Well thousands of glory spren surrounded dalinar as he was facing odium. And as they came to him, more and more all at once, his mental fortitude gained stronger and stronger. Strong enough to defy a GOD. That seems like the type of shardplate someone like Dalinar would need. Not physical. But mental.
