Magicka Necromancer in PvP is probably the worst spec out there for solo and small-scale play and this is highly tied to standardization and how the class (and warden before) has been designed.
With the necromancer class you get 3 skill lines one for each playstyle.
This is where the issues begin, with 5 skills and 1 offensive ultimate you can never manage to satisfy all offensive needs a class has to perform well in PvP and PvE and in different situations there be it dueling, solo play, small-scale, or running with a big group.
Those 5 skills are further thinned out in terms of viability for pvp as things like the skulls are exceptionally bad to begin with, a 300/350ms minimum traveltime means you will never ever hit someone even if you stun them in the gcd before (if you had a viable stun to begin with).
Not only that but it also deals only mediocre damage and has no proper secondary effect that would help it, a 20% damage increase doesn't help as you can't play around it, you can't just stop using your spammable because you want to keep the damage buff for when you want to burst someone, because then you will never be able to damage them beforehand which is mandatory with health pools being way too high.
The trend becomes worse when even more skills fail to perform at all in PvP, your dedicated "dot" in the form of the mage fails from the get go. If your target is running away it won't attack it, if you run around your mage will teleport to you and not deal any damage, if you'd like to focus someone who's not the closest target you're SOL with the mage and don't forget the dot has no secondary effect at all.
Now to the skill which gets hit the most by standardization, ofc we're talking about the tether.
In a game that wants to balance PvE and PvP together you will never be able to balance a skill like this as it's either useless in PvP or completely overperforming in PvE.
If you increased the damage enough to make it worthwhile for the effort you have to put in to hit an enemy player even once you'd easily had a skill that would outparse any other spec alone.
As of right now the tether deals disgustingly low damage, even if someone would stay in it for the whole duration he wouldn't even notice the damage as health regen would simply outheal it.
This leaves magicka necromancer with 2 class skills to use in PvP to deal damage and those are blastbones and graveyard.
Stalking Blastbones as we all know have no secondary effect apart from dealing 10% more damage because either they jump instantly or they never go off. Due to this behavior playing a burst combo around them is impossible, you don't want to play russian Roulette when fighting someone with an Assault rifle.
Now we have a single last skill to save magicka necromancers offensive presence in PvP and it actually does that somewhat, it's an unique skill that lets you activate the own synergy for great damage, but ofc there's a catch, putting it down on a player and hoping that he stays in it for you to activate that skill while you burst him is again reliant on your target to be a target dummy and not a player who will do anything not to stay in there. And if you miss it you have to wait 20 seconds in order to get a new chance.
All of this comes down to magicka necromancers offensive presence being cycling any spammable except your class one (last patch it was master destro but rip that or asylum force pulse) and blastbones and then you hope your enemy is grateful enough to just die to it and not simply heal back to full health in between your blastbones coming in.
Now some people might say, but you have a really strong ult that applies major vulnerability and deals a lot of damage.
But that's not the whole story in order for those 30% extra damage to make a difference you have to have damage to begin with and not a single soul stands in the colossus for more than one hit which reduces its damage immensely and makes your 225 ultimate into a glorified spammable hit which applied an overtuned debuff for 8 seconds. The issue here is, your target just got the message "hey i got 8 seconds to kill you, if you survive those I'll never be able to kill you" and they will just play defensive and there is nothing you can do about because you don't have a stun or meaningful damage outside of blastbones.
What makes things even worse is that there are 10 more skills in the necromancers toolkit and none of them will help it kill anything.
This puts necromancer into the odd situation of being completely over saturated in the healing and tanking department when it's absolutely not needed as both of those playstyles can be more than satisfied by a few morphs without taking out whole skills for the offensive playstyle. There's a reason we have 8 DDs and 4 support specs in raids and not vice versa. The same thing is true for skills.
That is why the necromancer class and also the warden class have to be freed from the bad corset of 1 Damage 1 Healing and 1 Tank skill line but be adapted to how the old classes work, they are what made the game and combat great and interesting.