So, what are Ground-types, really?
The Purpose of the Ground Type:
Ground-type, as mentioned before, was designed as a companion type for Rock. Rock was originally designed as a defensive type with some weak offensive capabilities, while Ground was an offensive type with great defensive capabilities. Ground was meant to buff terrestrial species, just like how Flying and Water did for their species, and to cover weak species with low power.
As things have passed, Ground-type became the primary type for the Earth element, taking over Rock completely, and becoming a symbol of power. While Fighting was hampered by buffs on Flying and emergence of Fairies, and Rock was hampered by Steel, Ground was made more powerful against all these events. Ground's sheer power also made it a good choice for three stage Pokémon, as opposed to its colleagues.
Ground doesn't still represent the element of Earth fully however, and until we see something like a Ground Stone we will still wait for Ground to become a primary type.
The Aesthetic Archetypes of Ground Types:
Species based on sand-dwelling Pokémon, these species traditionally get abilities like Sand Veil, Sand Stream, Sand Rush, Sand Force and the move Sand Tomb. Due to most desert species being mammals, they tend to be in Field Egg Group.
Species that live in caverns and dig tunnels, these are species associated with moves like Dig and Drill Run. They tend to be moles.
Species that live in mountainous regions like valleys and canyons belong here.
Other groups would be marshland-based species(Water/Grounds and Stunfisk), clay-based species(Baltoy and Golett-line), fertility deities and beach-based species(Sandygast-line)
The In-game Archetypes of Ground Types:
Early-game Ground-types: Lesser group of Ground-types, this group is generally controlled by weaker Ground-types around 425 range, though Excadrill is significantly stronger other Ground-types in its generation. They tend to appear in early caves.
Mid-game Ground-types: De-facto the primary Ground-type archetype, these tend to be three stage Pokémon. In odd games they tend to live in deserts.
Late-game Ground-types: Second most common group, these tend to be around 500 BST range, appearing in late-game mountains and Victory Road. They tend to be two staged, but some are three staged.
(Water/Grounds belong to Water's terrestrial secondary early game Water-type archetype).
The Stat Archetypes for Ground Types:
Watchtower: Ground-type's version of a wall, they tend to have offense enough to push back against its opponents.
Panzer: Ground-type's version of a sweeper, they tend to cut Speed for offense, or in case of Dugtrio, the reverse. They rely on hitting fast and hard, but have some defense to survive a hit or two.
T-34: Ground-type's version of a bulky offense species, these species often excel in offense rather than defense, though some might excel in defense in expense of Special Defense or vice versa.
All Ground-types are offensively oriented, and the type generally has high HP.