Apologies for the huge wall of text. TL;DR at bottom

Ever since the repeated (and arguably necessary) nerfs to heavy armor, magicka templars have been utter garbage in PvP. We used to be seen as unkillable BoL spammers, which was generally true with constitution and the + spell damage from heavy armor. It was pretty ridiculous. There was little or no reason to use light armor in PvP because templars are the only class in the game without inherent stamina sustain on a magicka build. Stamina sustain is necessary in PvP, especially for a class that has little or no ability to reset a fight or escape.

NBs have a passive +15% recovery. Sorcs get 20%. Magicka Wardens get stamina return from healing and DKs have two sources of inherent stamina sustain in the ridiculous Earthen Heart passives. Magicka templars? Basically nothing. We could slot Radiant Aura / Repent for the passive 10% but that is a waste of a valuable skill slot in PvP. Repentance is nearly useless now that we have to fight each other for bodies. Magicka templars are in a position that forces them, more than any other magicka build, to go for stamina sustain gear of some sort. Amber Plasm and Shacklebreaker come to mind. On a DK, for instance, the sky is the limit when it comes to gear selection. I don't have to worry about running out of stamina because Battle Roar and Helping Hands are more than enough to make sure I can always break free with a little self-control.

The stamina sustain problem wouldn't be that big of a deal if magplars weren't expected to essentially sit still to fight. Our "house" is built of twigs these days because we can no longer mask the shortcomings of our class behind heavy armor. We can still use heavy armor, but we can't really fight back in it. It's defensive only, as it honestly should be. If you want to compete in duels and versatile PvP, you need to be in light armor. Heavy armor magplars are healbots. It can be fun to be a healbot, but it's not fun to be essentially the only class that can't excel without the help of others.

That's the most obvious red flag with the templar, and the most annoying part of playing one. I'm very helpful with allies at my back because I can top off their health while they do their thing. My signature beam compliments any sustained offensive effort if I'm free to cast it. As soon as those allies are gone, I'm left with mediocre damage output and some neat self-heals. No interesting utility, no roots, no effective CC, no effective ultimates, no effective source of major debuffs, such as defile, and yes, no stamina sustain.

Yes, we have Dark Flare for defile, which will be "better" next patch, but Barrage is now the far better morph and landing Dark Flare is nigh-impossible against good players. You can write off the damage portion of the spell half the time, so even having a 100% chance to apply the defile after cast isn't enough to save this spell for PvP. We have interesting burst potential with Purifying Light, but what good is burst if you have no effective defile or stuns in your kit? Despite countless changes, Eclipse still feels clunky and useless, especially with the Total Dark morph doing nothing against CC immune targets. Unstable Core would be decent save for the fact that any player worth their salt is going to go on the defensive while it is up, meaning you're basically just giving the opponent free CC immunity and a telegraph of the next few seconds of combat. Or they can just break out of it and move on.

So we've established that magicka templars are too reliant on allied players and can't sustain stamina well. The stamina issue is compounded by our lack of escape mechanics. Sorcs can blink, NBs can vanish, and Wardens have reduced snare effectiveness, chicken wings, and stamina sustain to help them get away. DKs can root spam or just shrug off the damage while keeping their stamina in check. If a magicka templar is in trouble, they have to claw their way out of it. No speed boosts, no escape mechanics, just stand there and take it. We have good heals, sure, but they are easily hard-countered with defile. Yes, we can play a vampire, but that's yet another bandage solution. Yes, we can cleanse, but what good is cleanse with multiple players smacking away at you? You need that GCD for a burst heal if you want to get away. The magicka templar is one of the fastest classes to crumble when focused.

Our spammable, although I'm eternally grateful we have one (sorry Sorcs), again fits the theme of "good with others." If I'm fighting alone, I have little or no guarantees that I can keep the target in sight of the spell. Anyone with roots can avoid it with ease. I'm better off relying on my direct attacks like Vampire's Bane or Destructive Reach to land hits most of the time. Front-loading the snare would fix this. Give us the 70% on the first hit, not the last. Suddenly people have to work to get out of it.

Our ultimates are a disaster. Crescent Sweep is nice for stamplars in PvP, but Empowering is very unimpressive. The mitigation is decent and the cost is right, but it does little or nothing in terms of damage, especially because it's so hard to land the initial hit. There is no defile like Incap has, so the damage can be shrugged off, anyway. Nova is getting improved somewhat but will still be far too costly and ineffective against anything short of a zerg. Our healing ulti sure does heal. Meteor isn't an effective alternative because we are one of two (unless Permafrost does it) classes that can't break block. The destro ult can be good against zergs but it isn't a good choice for duels, as it has the most obvious telegraph one can imagine. We essentially have to use Soul Assault and hope it hits hard enough to make Power of the Light land a huge hit. If our opponent blocks or shields, it's not going to do much.

So that brings us to the PTS changes. They're good at addressing various unused skills, but our kit is still shoehorning us into a bland role that few people enjoy playing OR fighting in PvP. I will admit I love the Honor the Dead change, but that doesn't change my primary complaints. I don't want to be forced to hide behind my team and spam heals on them. I want to be able to compete in duels as well as being an asset to my team. I don't want to constantly fail to score kills while players escape with cool mechanics, just to turn around and be annihilated the second I find myself outnumbered, because I don't have said cool mechanics. With the current state of the game, I'm outgunned by everyone. There is nothing interesting setting my class aside from others aside from heals and cleanse, both of which being somewhat obtainable through universal skills and gear. My passives generally don't compare to those of other classes, save for a few. Crutchgore alone has given every other class a huge burst heal. I'm forced into fewer sets and loadouts to compete at all. It's boring. It's frustrating.

TL;DR version:
Stamina sustain massively sucks
Ultimates are garbage
Lacks utility (buffs, debuffs)
Lacks effective CC
Abundance of clunky skills
Can't hard reset a fight (healing doesn't count as a reset because the flow of combat hasn't been interrupted)

But hey, at least I can stand behind my NB friend and beam / BoL repeatedly, hoping the enemy team doesn't take notice.