I think the main issue is that Vengeance it is extremely comp reliant. A Frost mage is mandatory because Vengeance kiting is actually really bad without a personal spammable AOE snare whereas Blood has a lot more flexibility in comp since it kites better on it's even with it's shit mobility because of the almost spammable 90% snare. Basically Vengeance is much more reliant on the team and their abilities than other than blood which has a tool for situation. 1st boss in Tol Dagur is aids as blood on necrotic. Only situation i've felt helplessNDdependent on teammates. where as on vengeance you just roll over dead if the group doesn't peel for you on trash packs during spikes downtime or have a really on point healer on certain tyrannical bosses.