Okay, so I think it's important to point out that there are cultural connotations to the Fighting and Dark types in Japan that don't necessarily translate over well to other countries. The Fighting type represents more than just being physically strong or good at fighting through any means necessary, it also represents a sense of honor that is held in high regard in Japanese martial traditions. This ties into the warrior code of bushidō, most versions of which put a heavy emphasis on honorable conduct. As such, straightforward, face-to-face combat is glorified in many ways in Japanese culture; the Fighting type represents this, as most Fighting types are depicted as stoic and honorable.
On the flip side of this is the Dark type. It's pretty well-known that in Japanese, the Dark type's name actually translates to Evil type, and this is no accident. The Dark type generally represents the opposite of the Fighting type; dishonorable, deceptive, and unfair tactics. Dark-types are usually depicted as cunning, aggressive, and deceitful, as are most Dark-type moves. It wasn't until Gen 4 that we would get a Dark-type move that actually involves the concept of darkness as in a lack of light in Dark Pulse, and even then Dark Pulse is described as negative energy.
Incineroar is a heel fighter. In short, he's the bad guy wrestler who often uses dishonorable and unfair tactics. This is why he's a Dark-type; it makes perfect sense when you consider the cultural connotations behind the two typings. Many of the other Pokemon you posted, especially the Swords of Justice, represent the honorable side of the Fighting-type. Electivire is usually depicted pretty neutrally in this respect, neither as a particularly honorable battler nor a particularly deceptive one, so it having neither typing also makes sense.