Knight
The greatest strength of the Knight is its ability to provide your team with excellent defense in any situation. Specifically, the Knight effect will block damage from all sources, regardless of the type of damage, whether it’s from basic attacks or champion abilities. Furthermore, all champions in your team benefit from this effect so backline carries will survive better with the presence of the Knight class.
In terms of team composition, Knight is quite friendly for players with “low luck”. With 4 units Poppy, Leona, Nautilus, Thresh all costing only 1-2 gold, it is relatively simple for players to upgrade them to 2 stars at levels 6-7. These units will help players maintain a solid front line to keep health and gold during the mid-game. After that, players can freely choose carries and team compositions depending on the flow of the match.
Armor
Although it only has a very simple, easy-to-understand effect of providing armor for the whole team, the Armor class is still favored by many players. With the rise of physical damage-heavy compositions like Assassins, Marksmen, and Cannoneers, the large amount of armor from this class is absolutely necessary. With just 2-3 champions, you can get strong defensive stats from Armor, allowing players to pivot to many different team comps while still ensuring durability for the team.
Not stopping there, the Armor champions themselves are also extremely powerful units in terms of crowd control, tanking, and dealing damage. For crowd control, players can rest assured that the duo of Rell and Nautilus will accomplish this task well. For Jax, after receiving a minor buff in season 5.5, this unit has also shown to be significantly stronger and can take on damage-dealing responsibilities. It is this versatility that makes the Armor class incredibly hot right now.
Demon
If you pay attention, the Demon class has been a powerful trait since season 5 and has been continuously nerfed by the Teamfight Tactics design team. In season 5.5, the health restored upon revival for Demon units was also nerfed to 25/45% at 2/3 units instead of 40/75% as before. Despite this, the Demon class still proves to be overwhelmingly powerful, helping compositions like Assassins, Undead, and Mystics secure top positions in the season 5.5 meta.
Explaining the current situation of “nerfing continuously yet still strong” requires us to acknowledge that the quality of the Demon units is too strong. In terms of crowd control, Volibear and Ivern are top-tier champions in the current meta. For damage dealing, Nocturne and the new unit Fiddlesticks also prove to be extremely strong with their wide area damage skills. Perhaps Riot needs to directly nerf the power of Demon champions in the future to reduce their overwhelming dominance.