Acid Fiends have sucked since forever. What if instead of Elvensong being the synergy that grants avoid through Symbiosis, its Poison Flash instead? This would give a bit them more life through the existing synergy to Acid Fiends. Then, since several other summons from other classes gain awesome buffs through other passive skills in their respective trees, fiends could gain the benefits of Symbiosis. The 100% life regen would be too op at 20 seconds, so maybe 10 to 20% effectiveness for that specifically, but 20% avoid would make them much more useful in late game. As is it now, they get destroyed way too quickly, and its a bit too costly damage-wise to be filling gear slots with summon gear.
Swapping the lighting spell damage to any other spell damage (poison????????) for the Mythal/Symbiosis synergy would be a nice improvement too. The lightning spell damage is kinda pointless since only 5 people are going to play Stormfront builds per ladder.