When you combine these changes along with the sustain difficulties a lot of people have with the Necro means they are no longer as important or vital.
Necromancer Tanks while not offering as much group utility as they didn’t previously are still incredibly good at generating Ultimate which now is probably one of their biggest strengths. The Necrotic Potency skill means Necro Tanks can build their Ultimate incredibly quickly and this is a factor to consider in a wide range of situations. A Necro being able to create their own corpses with skills such as Blastbones, Skeletal Mage, Beckoning Armor and Spirit Guardian means even when in combat situations like boss fights where there are no corpses for long periods of time, a Necro can make their own.
Necromancer Tanks have two good class-based Ultimate’s with Frozen Colossus and Renewing Animation. Colossus provides Major Vulnerability, which was once a Class buff, but is now easily obtainable from other sources such as Turning Tide and Archdruid Devyric gear sets. Some groups might not use these sets however and then suddenly there is a requirement to have 3 Necromancers in a 12-person Trial group. If those sets are being used, then this Ultimate is not really needed anymore. Renewing Animation is a great help in beginner progression groups because sometimes it just means you don’t have to wipe a fight and start again; you can resurrect 3 people and potentially continue. This works especially good in those progressions and when doing random groups for dungeons, if your whole group is dead, you can resurrect them with 1 skill.
Groups buffs that you can provide with a Necromancer Tank include Area of Effect Minor Vulnerability which means that enemies take 5% increased damage, this can be achieved in many other ways in the game also. As a Necro you can also supply your group with Empower via Empowering Grasp, but this is no longer as strong since it buffs Heavy Attacks by 80% rather than Light Attacks meaning the Necro Tank has lost a really big part of its usefulness in group content.
When it comes to healing, the Necromancer Tank has a decent self-heal. Scythe heals based on enemies hit meaning the more enemies hit, the bigger the heal. This can be a big problem also when you are 1vs1 with a boss and it moves such as in Cloudrest, during the transitions you have no way to heal effectively. There is a heal over time with the Spirit Mender but again it’s unreliable due to the fact it can heal someone else and not you.
Mitigation is a strong part of Necro. You have access to the Spirit Guardian which absorbs 10% of your incoming damage and it has 30k health. There is also the Disdain Harm passive which reduces your damage take from damage over time skills and a lot of the newer content is very dot heavy so reducing that by 15% is so helpful in some of the really difficult Hardmode Trials where incoming damage is extremely high especially from DoTs.
Sustain has improved for Necro Tanks but is still way off compared to every other Class. You have Mortal Coil which will supply you with a small number of resources every 2 seconds but that’s more or less it’s only function, so it takes up a valuable skill slot for a tiny amount of resource gain when compared to something like the Templar which has Restoring Focus which offers large amounts of healing, Major Resolve and resources every second, it’s seeming a waste to even slot it. The Death Gleaning passive is also useful but only really effective on add pulls.
The Necromancer Tank was once the most requested Off Tank for trial content has become quite ineffective and unnecessary with recent updates. From a beginner point of view, it’s hard to play compared to most other Classes mostly because of the sustain issues. Although a lot of people find them fun to play there is very little reason to do so at the moment, even for 4-person content they are not quite as good as other Classes.