What makes Soulshine so good compared to sets like Julianos?
Higher spell damage for channeled spells (ie both of Templar's spam options are channels, and so is their execute) However, you're still giving up either light armor passives or arcane on your jewelry to use this set.
To the OP, heavy armor is always going to be lower dps for PvE than light armor. There are some dps-y options for heavy armor sets and you can certainly push acceptable damage for dungeons with a good rotation and good sets with heavy armor, but there's not really places in a normal dps build where you could give up defenses for more damage than it already is.
If you're speaking of PvP or soloing things (overworld, dungeons, vMA, whatever), yeah go ahead and rock heavy armor, the defense and sustain is good and the damage buff is okay if you're taking all the hits.
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Pve will require you to use 5 light armor/1 medium/1 heavy with dual wield front bar and Destro back bar for aoes. The meta is currently 5 Burning Spellweave, 5 Moondancer, and 2 Grothdarr. I don't have easy access to Moondancer crap, so I'm using Julianos. You'll want swords for DW for the spell damage buff.
For PvP, heavy armor is amazing on templars. You can play with a variety of sets.
"Buzz Lightyear toy isle shot" Stormcalling/Animal Companions/Assassination PVP build hater