Among all Pokémon and all generations, there are 84 total bug-type (pure bug and half-bug) Pokémon, which equals 9.35% of all Pokémon. However, among these 84 Pokémon, there are some who simply look like they shouldn't be there.
Primarily due to appearances, but also based on their teachable moves, and with bug-type being considered by most fans as one of the weakest types, some Pokémon would get much stronger if they had their bug-type exchanged for something else. And most importantly, they should have their type exchanged because it doesn't suit them.
Masquerain
Masquerain's previous form, Surskit is bug and water type. When it evolves to Masquerain, since it gains wings it exchanges its water type for flying.
However, it would make more sense, based on its previous form, its appearance, and its moves, to give up its bug type instead during evolution. Making it water and flying type on evolution would be more suitable for Masquerain than maintaining its bug type.
Golisopod
Golisopod is a bug and water type Pokémon introduced in Generation VII. Its appearance resembles a huge, white-colored, purple-eyed alien. Solely based on its looks, it does not seem to suit a Bug-type nor even a Water-type.
Instead, a psychic, steel, or fighting type would be more pairing with its style. Even a ground or rock type would be more suitable than bug and water.
Shelmet
Shelmet is a pure Bug-type Pokémon with an appearance that literally resembles a shellfish. If Shelder, which looks like a clam, can be a pure water-type Pokémon, why is Shelmet a bug type?
It should be either a pure water type or perhaps a mix between water and rock due to it being a shellfish and residing in rocky beaches. But bug definitely makes no sense.
Accelgor
Accelgor, Shelmet's evolution is also a pure bug type, and it doesn't make any more sense than Shelmet. Based on its appearance, which looks like a mysterious psychic fighter from some kind of sci-fi movie, and some of its later moves, Accelgor seems much more suitable for a fighting or psychic type.
Even being a poison-type would be more fitting(or any combination of the three types) compared to bug.
Dwebble
Dwebble is a fan-favorite bug and rock type Pokémon which has the form of a living seashell. Similar to Shelmet, its ideal location would be rocky beaches.
Although the rock type seems to match perfectly, it would be more suitable to pair it with a water type instead of a bug type. A seashell is far from a bug, and due to it living next to the sea, or even in it, there is no reason to not change it to a water type.
Armaldo
Although Armaldo's previous form, Anorith is fitting for a bug type due to its bug-shaped body, Armaldo is far from that. As a blue-colored, tall, strong, beast-like monster, Armaldo doesn't feel right being a rock and bug type Pokémon.
Although the rock type seems fine, the bug type doesn't. It should either be a pure rock type, or more fittingly have water or steel as a secondary type since it has some moves of these types.
Crustle
Crustle, the evolution of Dwebble, is a bug and rock-type Pokémon. However, for reasons similar to Dwebble, it doesn't feel right. It is something between a crab and a living seashell and can be found next to the sea.
Even if what it is underneath its shell could resemble a bug, depriving it fully out of either rock or water type seems simply unfair. It is weird having a Pokémon like Crustle or Dwebble and being unable to teach it Surf or Waterfall.
Escavalier
Escavalier, an evolution to Karrablast, is a bug and steel-type Pokémon. Although its previous form resembles a bug accurately, Escavalier's appearance does not. As a steel-covered, warrior-resembling, lance-bearing monster, bug-type does not describe it properly. While steel is fitting, it would be better if it were either on its own or even better combined with fighting type.
Since Escavalier gets some fighting moves as it levels up, and since having it as bug and steel makes it two times more weak against fire, the bug type doesn't really fit and is more of a weakness.
Genesect
Genesect, one of the strongest mythical Pokémon of Generation V, is a bug and steel type Pokémon. However, its appearance tells otherwise. As a tall, purple-shaped, alien-like Pokémon, it seems ideal for either the psychic type (like Mewtwo) or the ghost type (like Gengar).
This would make it far more efficient in battles and its appearance would match its types. Having a mythical, and well-respected Pokémon die easily by fire attacks without having a chance to fight back at all, isn't exactly what players expected from Genesect.
Forretress
One of the biggest surprises that new players faced when starting Pokémon was Forretress. What seemed to be a massive fort-shaped Pokémon with exceptionally good defense stats, turned out to be a bug and steel type, which is insanely weak to fire attacks, one of the most common attacks in the games.
Forretress turned out not to be the defense monster that players were hoping for, primarily due to its bug type. Its appearance would be far more fitting for a rock or ground type, and such a change could make it as strong as it looks.