For the first one: Dark as a type has always been limited in a way that the other types haven't really been limited: it doesn't have a single, really strong, spammable attack. You could argue Rock and Steel falls into this boat as we've all had Stone Edge fail us when we really needed it to not fail and Iron Head is piss weak but at least Stone Edge has power and Steel was always intended to be defensive. The strongest non signature move Dark has is Crunch (especially now that Sucker Punch has been weakened). Dark types also have the consequence that their new spammable move weakens if it's used against a target that doesn't immediately die to it (it's totally possible for Krookodile to lose to Necrozma, for instance, if it doesn't have a boosting item and only has Knock Off as a Dark-type move). Not to mention that Mega Evos and Z-Move users will not feel the added effect and most Z-moves in particular can heavily punish Dark-type users trying to take advantage of their opponent's weakness (scenario: Latias takes 70-80% from a Scarf Krook Knock Off, reveals Dragonium Z and kills with a Z-boosted Draco Meteor). Fire, Water and Grass have options across the board, Fighting has something for even trash mons and we don't even need to start with Dragon. Now, other conditions I can say have heavily benefited Knock Off include the removal of Steel's resistance to Dark, which seemed a little unnecessary and harmed mons like Jirachi. But this is not a viability ranking thread. I think Knock Off is fine as it is and Dark as a type has heavily benefited from changes over the past 2 gens.Some things that have bothered me:
Buffs to Knock off The Base power buff is fine, but I feel that the 1.5 boost in power when Knocking off an item really is too much, especially since the penalties of losing an item already are so huge.
Imbalances in the game between physical and special attackers Physical attackers in Pokemon suffer from noticable restrictions that special attackers barely have to worry about. Most physical attacks are noticably weaker then their special couterparts and usually when they are strong, they suffer from major penalties such as Stat drops and recoil, wheras the only penalties most special attackers suffer from is imperfect accuracy. Additionally, Physical attackers are almost completely crippled by Burn and Intimidate, moves that special attackers almost never have to worry about.
Physical attacker penalties: I agree with this, but physical attackers do have their own boons. There's only one special attack, for instance, that is boosted by Tough Claws. There is no special equivalent of Return or Frustration, which has served as a coverage option for barren-movepool mons (Gen 4 Azu anyone?) and as a STAB option for the type-change-ability mons like M-Glalie/M-Salamence/Golem-Alola. There is (at last) special equivalents to Defiant and Moxie (Competitive and Soul-Heart) but both are incredibly limited. Finally, while physical boosting moves are not diverse, they are well distributed (how many mons can learn Swords Dance or Bulk Up via TM?) Calm Mind remedies this but Nasty Plot is thinly spread and Quiver Dance equally so. Special attackers do need some kind of curbing but they also miss out on cool buffs the physical side has.