You get 4 guaranteed high light/power items in the raid, +1 with challenge. If you do Prestige instead of Normal, you get loot from both Normal and Prestige. It's more effective than doing 1x Normal and 1x Prestige. Very high chances of your cloak dropping at least once. It also looks fancy, maybe you'll even keep it instead of infusing. The loot from other sources is just very random, as it also drops from a huge pool. The chances in the Leviathan are better because the loot pool isn't that huge. Or you keep praying to RNGesus for the other milestones.