So, what is the Ground-type?
All JRPGs have some sort of Earth element, except maybe SMT(though DDS and Persona 1 and 2 has it). This is because both Chinese and Greek elemental table contains the earth element, but Chinese version has Earth as the fifth element, while Greek version has it one of its common elements. However, Earth is more commonly associated with enemy types, which is why in Pokémon Ground-type is a powerful and common but non-primary element.
Nonetheless, Ground is most efficient offensive type solo-wise alongside Fighting, and like Fighting has a type that is immune to it, Flying(in allusion to Air elementals and avians being immune Earth magic in some RPGs). Ground is also greatly associated with Electric, and serves its antithesis, though unlike Electric it is not considered a primary elemental type.
It might have been that if Rock and Ground were not separate types Ground would have been a successful primary element, but that wasn't the case, as Rock was designed initially as a defensive type that served as an early boss-type, while Ground served as an uncommon type that would help statistically weak species. This is no longer true of course, so there is nothing stopping Ground from becoming a primary type.
The History of the Ground-type:
Original Ground-type was a companion type to Rock-type, allowing it to gain more resistances and offense at the expense of being weaker to special moves. In the original games, Ground was heavily focused on physical and was heavily weak on Special side, in allusion to Fighting and Rock. Because Steel-type didn't exist in this generation, Ground was associated with Fighting as the Earth trio. Because of Ground's tremendous power, most Ground-types were either too weak or too strong.
In this generation, Ground-type had the strongest physical moves, Dig, and Earthquake, which were not only available for Ground-types, but all other terrestrial species. In this generation, Sand-Attack was still Normal-type, and there was no Mud moves, but Bone Club and Bonemerang remained signature moves for Cubone and Marowak.
The new generation hampered Ground-types significantly. Many species got either equivalent or weaker Special moves, particularly in Special offense, which sealed the type as a physical type, just with a bit better defense than Rock. This was largely done so the species introduced previously could be buffed through other means, like Thick Club, which made Marowak one of the most powerful Pokémon in the game, though briefly. Introduction of Steel and Sandstorm have been a massive blessing for Ground-type, unlike Rock-type which was hampered by it. The first Water-Ground species, Wooper-line, was introduced here.
Sand-Attack was made into a Ground-type move and Mud-Slap was introduced, though it was made available through Falkner, a Flying-type Gym Leader. Dig was debuffed, at the expense of creation of Magnitude, a mid-game Ground-type move that serves as the earliest Ground-type move most Ground-types can get these days. Marowak gained a new signature move, Bone Rush, which was later granted to other species. Spikes was introduced, which served as the herald of future entry hazards.
The next generation was better for Ground-types. While Sand Veil was the only move that was relevant to type, the type got its best Ability Arena Trap this generation, which made Dugtrio immediately a threat despite its lack of power, and helped Trapinch to hold on on its own. Water/Ground was popularized, which lead to creation of more Mud based Ground-type moves, and more desert Pokémon were introduced for this generation overworld weather effects, which lead to creation of Sand Tomb, Ground-type version of Fire Spin.
Ground-type also enjoyed a mascot legendary, but it remained more of a Fire-type, and one of the rare type combinations introduced here, Bug-Ground was exclusive to an uncommon and weak pre-evolution.
Special-Physical split helped Ground-type immensely, but Ground-type remained physically focused. One more Mud based move was introduced which alongside the previous ones was made a Special move. Earth Power was introduced, and made into a Tutor. However, there wasn't much of a new Ability besides Hippopotas-line getting Sand Stream, Tyranitar's ability. Ground-type also gained another starter, Torterra, and a pseudo-legendary, Garchomp.
Gen 5's Weather Wars made Ground-type a beast. With new Abilities like Sand Rush and Sand Force, and insanely powerful Excadrill, Ground-types became an absolute terror. They failed to fight against Water's Rain, but they hold their place. New moves with wider distribution, Bulldoze and Drill Run were introduced. And one of the best competitive species in the game, Landorus, was introduced.
Ground-type's association with deserts and swamps were made into actual regions with the new region, Unova. Its association with clay was also revived, leading Golett-line.
Gen 6 was not significant for Ground-type, though one of the most famous Ground-types was introduced in this generation, Zygarde. Zygarde only became relevant later, however. A new Ground-type, Diggersby, was introduced, and remains to be the best early rodent in the game. This new species also brought in Rototiller, building on Landorus' association with fertility. Ground-type did not get much Megas, however, though they were decent enough.
Gen 7 buffed Zygarde into a true power, but it remains underutilized. New moves like High Horsepower, Shore Up, and Stomping Tantrum were introduced but lacked distribution. New abilities like Water Compaction and Stamina were introduced to abuse the type's defensive qualities, but they remain insufficient. Many Ground-types also gained Alolan forms, most of which do not remain Ground-types. This was the third time Ground-type was replaced by another type. Dugtrio got some notable buff though not much.
The Overview of Ground-types:
Ground-type have evolved from a de-facto companion type into a proper elemental type, but there is still work to be done. Ground-type still remains predominantly a secondary type, and many species dispose of it after evolution, despite its power. Its combination with its common ally, Rock, is one of the most infamously weak combinations, while its associations with its antithesis like Ice, Electric, Flygon are some of the strongest combinations around.
Ground-type have also evolved from a type of extremities to a large variant of accessibility, from start to end of the game. Ground-type still remains a bit rare not in numbers, but in terms of families due to Ground-type's abundance of three-stage evolutions, and recent two generations have not introduced a sufficient amount of Ground-type.
Ground-type is also missing a fair amount of type combinations and typings, which will likely appear in the future.
(Mani you would think you would find more to speak about your favourite type but sadly I'm out of ideas.)