Gear Review and Alternative Setups
I found Bahsei/Siroria to be the best setup, barely edging out Bahsei/War Maiden. If you can't stand still I would just go War Maiden over Siro, although if you're in a fight where you have to hold for destro for cleave, I would go with MS or Medusa, since destro is unaffected by War Maiden.
And of course you can run Medusa if you need bar space. If sustain is bad you can always put on False God's Devotion too. Just make sure you have a Minor Slayer set on whenever possible. Acuity looks good on the dummy, but personally I wouldn't recommend it in raid.
As with any other setup I've got Harpooner's Wading Kilt and 1 Slimecraw on, if you can't run Kilt go Za'an, if you can't run either (or can't run Kilt and want higher cleave than Za'an) go two crit pieces.
Sustain is good enough that you can run 5 light/2 medium. Purifying Light doesn't scale with Bloodthirsty, but Radiant Oppression is so strong that Bloodthirsty beats Infused anyway. As far as DW vs Inferno goes, you should be staying in melee range if you're playing a Magicka Templar. Puncturing Sweep is so much stronger than any other spammable you could run that if you can't stay in melee range you're going to lose a ton of DPS. Because of that, DW should be a viable option for most fights, and I would recommend running it over inferno.
Skills Review
If you can't run Sweep you can go with Elemental Weapon or Force Pulse and watch as your DPS hits the floor. Dawnbreaker/Meteor, Dawnbreaker/Dawnbreaker, and Crescent Sweep/Dawnbreaker are all good options for your ult, you can also go Destruction Staff Ultimate for burst phases/cleave.
If you're in War Maiden go with DB or Crescent Sweep over Meteor. If you have a Necromancer support giving you Empower, drop solar barrage for either ritual or orb. On the dummy you need either Channeled Focus or Spell Symmetry for sustain, in raid I would pretty much always go for Channeled Focus over Spell Symmetry, if sustain is good enough that you don't need either you can slot Ritual of Retribution or Mystic Orb instead. Lastly you can drop Inner Light for Camouflaged Hunter if Minor Berserk uptimes are low, as long as you're using traditional Spell Power Pots for the Major Prophecy.
Rotation Explanation
Opening is Potion > Dump Magicka to about 50% > Channeled Acceleration > Channeled Focus > Solar Barrage > Destruction Staff Ultimate > swap to the right skills > Blazing Spear > Light Attack* > Wall
*First light attack is between spear and wall, make sure not to walk up until you cast spear so that solar barrage doesn't hit early.
After that it's a very simple static rotation:
Purifying Light > 5 Sweeps > Purifying Light > Solar Barrage > Wall > Blazing Spear > 2 Sweeps > Repeat
Cast Barbed Trap dynamically in place of any Sweep.
Channeled Focus you want to cast after Purifying Light so you don't have to swap off of Sweeps. An example: you'd go Purifying Light > Channeled Focus > 4 Sweeps.
You can do the same with Meteor. If you're using DB or crescent sweep you can replace any cast of Sweeps with your Ultimate.
By far the biggest way to squeeze more DPS out of Magicka Templar is to make sure you're weaving Sweeps correctly. You can queue up your Light Attack and your next cast way before the animation of jabs ends. I very strongly recommend using Combat Metronome or a similar addon to improve your Puncturing Sweeps weave, this may be harder with higher or inconsistent ping. If you don't have access to addons, you can definitely make an observation by practicing the cast and watching the animation.
I started execute a little early in the parse shown below, the best place to start is 20-22%. Switch to using Radiant Oppression instead of Sweep. You shouldn't need to recast Channeled Focus for sustain in execute. Solar Barrage you should drop as soon as you start beaming, Purifying Light you want to drop around 15%, Blazing Spear around 10%, and then drop Wall/Trap around 5%.
Craft
Warfare
Fitness
Champion Points Review
Fighting Finesse and Biting Aura are very close, you can run either, and if you can't run Backstabber go with Master-at-Arms/Deadly Aim/Fighting Finesse/Biting Aura.
Introduction (Update 31, Waking Flame)
MemeDankExtra from PC/NA helps us showcase the damage potential of PvE Magicka Templar damage dealers in The Elder Scrolls Online.
Recommended race for this build is Khajiit. Altmer is an alternative choice. Khajiit and Altmer are very close, either one is fine, Khajiit is nice because of their racial passives that offer extra Health and stat Recovery.
Recommended Mundus Stone is The Thief.
Recommended potions for this build will be Essence of Spell Power. Meme used Breach Potions to get more sustain by being afflicted with a negative Status Effect to gain the benefits of the Champion Point Slottable, Sustained by Suffering. He does not recommend using this potion in actual raids for obvious reasons. If you're getting Major Sorcery from a Dragonknight using Igneous Weapons and have Inner Light double barred you can run Heroism Potions for more ultimate gain.
Recommended food for this build is Ghastly Eye Bowl or any bi-stat food (Health + Magicka) for content that requires you to do so. You can also do Clockwork Citrus Filet or Witchmother's Potent Brew if need be.