On Malefic Grasp vs Drain Soul, I only analyzed their description, so if Drain Soul does more damage, then the spell's description must be bugged or misleading, since DS ticks for 2x more but every 2 second when MG ticks every second, and you completely ignored this. DS's own dmg of course is 2x more, so now I definetely think the tooltip of the spell is wrong, can't possibly tick for more than 4x. (I wrote what I wrote based on that)
You also ignored that refreshing ua and corr will not refresh agony, so after 2 soulburn or ua+corr you need to refresh agony anyway. Also refreshing ua+corr do