All this talk about atium makes me wonder would a fifth oath truthwatcher be a better match for the lord ruler considering their implied resonance. On that vein, do we know if shardplate can mess with atium or not? Considering burning electrum reduces or negates its abilities. it's not too much of a stretch to consider, with shardplate negating surges and all.
Also I think dalinar with his fifth oath would have enough investiture in his plate to resist the push of the lord ruler. Especially with the stormfather as a shardblade giving him the potential to wield the investiture of a large shard of honour. Though I don't think he could beat the lord ruler just be able to put up a fight.