no way, keep it on the pit and just muscle through it. want an easy fight, use a shit ton of mana burn, or even vortex. The siren has "frost arrow" which deals 1500 spell damage, for like 500 mana a cast. burn her mana and there is no damage that fight.
AMS is "what you see is what you get." 4000 spell redux doesnt care about your 50% reduction. it is just 4000. Which can be amazing, when used right. can also be 90% useless if used wrong.
Also, as this skill is leveled, the focus'd player takes less and less damage, while the allys take more; so REALLY, you would wanna focus the guy with the highest spell reduction, then look at armor. If their armor ranges 50-80, and he is in the mid for armor, but has higher redux than the others; focus him. The majority of the damage will go to the others; damaging them FASTER than it damages your target. HP is an important factor here as well. An HP tank with 20k HP, is a great target. Someone with 3K HP and 35% evade, and 200 damage reduction... is a bad target!
^^So, when used with the right players, and a team leader, and possibly vent; this is the best team skill in the game. When used with pubs; you might as well drop your items and leave.