To be clear, very few games are balanced quite as well as Diablo Immortal. In previous franchise entries, some classes could take on challenging twenty to thirty times as difficult as other classes in the rifts, creating a massive disparity between player options.
Things aren't so badly imbalanced in Diablo Immortal. Skills, gems, and gear, it's all been toned down and fine-tuned to prevent any class from falling off of the map or leaving the rest in their dust. Even so, it's clear who the chart-toppers will be unless balances and/or nerfs intervene.
S-Tier
Wizard
The Wizard is ranking at the bottom of many charts. They all admit it has the best damage in the game, but take exception to it being not tanky against demons. So what? Without a hardcore mode or severe death penalty, being able to destroy an entire rift's inhabitants as fast as possible flatly matters more than longevity. Especially since the Wizard can slay opponents faster than they can run toward them.
Against human opponents, the Wizard is the most important asset on the team, capable of dealing unprecedented group and burst damage, the most critical kinds of damage for a PvP match. With respect to those dunking on the Wizard, this isn't Diablo III anymore.
Crusader
After reading the rationale behind the Wizard, why is the Crusader breakdown, with its survivability and support, in such a high esteem? It might not be able to match the Wizard in solo rifts, but in group rifts, the Crusader has support skills that no other class has. And every warband will want at least one such unit.
In PvP, the Crusader is infuriating, protecting their precious teammates one second and then tanking as soon as the aggression turns against them. In the past, support has been left to the Monk or Barbarian. Now, that role is exclusively and adequately filled by the Crusader.
A-Tier
Necromancer
The Necromancer is likely a bottom-tier hero when left as a summoner. While it's great for solo play, rifts, and early game grinding, the damage from minions falls off due to a lack of intelligence and focus. But if the Necromancer has a party, they can drop the summoned units in exchange for powerful spells that rival a Wizard's output.
At the maximum level, the Necromancer has only one skill that affects movement and it's not a very well-liked or well-used one, so PvP can be an issue for those who get caught away from the pack. Still, with great team coordination, the Necromancer can be the primary damage element when supported and protected.
Demon Hunter
The Demon Hunter has a lot going for it with the range and mobility and only suffers from needing to both reduce armor and increase damage, making it split attribute focus in a way the other caster units don't have to. But with some increased survivability, many Demon Hunters will happily make that sacrifice.
Player combat is where the Demon Hunter, shines the most, able to get around meaty tanks, pick off casters and supports, then get back behind the frontline before the team can retaliate. With great burst and sustained damage, Demon Hunters have a huge tool kit to take care of monsters and human-controlled units alike.
B-Tier: Barbarian, Monk
Barbarian
Melee attackers are in a tough situation in Diablo Immortal. Without the crowd control abilities and disables from previous franchises, anybody attempting to tank in the traditional sense is going to die a good chunk of the time. That's fine if the damage is top-tier, but the Barbarian's physical damage isn't quite there yet, especially next to the other DPS sources after breaking the class down.
In battlegrounds, the Barbarian does have the benefit of mobility and meaty attributes, but many teams have taken to ignoring the Barbarian and dealing with more dangerous classes. They can certainly top the charts in the hands of a pro, but the same pros can make any class look good.
Monk
The Monk has the same disadvantage over the Barbarian with an emphasis on physical attacks, but it's dragged down by having skills that require predictable enemy locations and movements and a lack of personal movement. As soon as demons get frisky and mobile, the Monk is in trouble.
There is perhaps no unit worse than the Monk in PvP right now, veteran players will miss the support it once brought to the team. With a lack of the Demon Hunter's mobility or any other caster's raw damage, it seems the Mink is stuck in a confusing place where it has no real role to fill.
Diablo Immortal is available now for mobile and PC.