The Purpose of the Grass Type:
As previously discussed, Grass-types' primary purpose is to become an early-type for cleaning some of the key early types like Water, Rock and Ground, and through its resistances clean Electric as well. The other purpose of Grass-type is to spam status moves and leech off opponents' HP. Because of this, Grass-type is predominantly a defensive type, so even the offensive and speedy Grass-types have some decent defense.
Grass-types can be obtained easily in all generations in the early-game, unlike Fire-types and Water-types. The difference is, even if Grass-types are obtained later in the game, they still tend to be weak, as they tend to be single staged, or have unique abilities/types that render high stats pointless.
Much like Fire-type, Grass-type is supposed to be replaced around mid-game, as after that point the difficulty spike for Grass increases. Water generally fulfills this role, with Electric filling in the role of Water-type cleaner. However, because of its versatility Grass-type can be used for the entire game, especially since once you obtain it, you will be able to easily grind it.
The Aesthetic Archetypes of Grass Types:
Grass types are generally Green colored with some Brown colored, but there are other colors as well.
Conceptually, Grass-types can be divided into following archetypes:
Generally composed of animals with plant covering, symbiotes generally depend on the "host" body for additional moves. They generally lean towards Normal-type moves.
Mushroom, as its name stands, are Pokémon made of or infected by mushrooms. They get Spore and generally have access to Poison moves and Effect Spore ability.
Composed of Pokémon that have blossoming flowers, and learn Petal based moves. They have some association with Fairy-types, generally speaking.
Composed of Pokémon with tree shapes, they tend to get Wood Hammer.
Fruits and seeds:
Composed of Pokémon with nut or fruit shape or covering, they tend to get moves like Seed Bomb, Rollout, Sweet Scent and Worry Seed.
Lesser archetypes include cacti(Cacnea, Maractus), nature sprites(Celebi, Tapu Bulu) and cottons(Hoppip-line and Cottonee).
The In-game Archetypes of Grass Types:
-Early grass type: The archetypical Grass-type. With that, I mean THE archetypical Grass-type. Generally around 480-490 BST range, with higher ups being in 510-531 range. The first three odd generation variants were version counterparts to each other, but Gen 7 haven't repeated that.
-The mushroom: An odd generation archetype, these Pokémon tend to be two staged and have access to Spore. They tend to be 405-465 range.
-Secondary early Grass-type: Generally occurring in even generations, these tend to be gimmicky Grass-types in 425-450 range.
-Single staged mid-game Grass-type: Generally occuring in odd generations, they are single staged Pokémon that occur in the mid-game appearing in rare routes. Two of them, Tangela and Roselia, gained additional evolutionary lines.
-Late-game Grass: Generally occuring in 490-535 range, these are late occuring Grass-types with odd types.
-Mid-game Grass: Generally occuring in mid-game and in odd generations, these are Grass-types that occur in the middle of the game. They tend to be around 474-495 range.
The Stat Archetypes for Grass-types:
-The Tank: Generally focusing on defense and offense in one specific area, these tend to be slow, bu they tend to have abilities or moves to double their speed.
-The Wall: Generally focused on Defense, these tend to be good in both defenses. They use Leech Seed and Synthesis to restore themselves.
-SubSeed: Generally focused on being an Annoyer, these Pokémon tend to have high Speed with mediocre offenses and mediocre defenses.
-Dual Offense: Generally focused on both offenses, these Pokémon tend to be either bulky but slow or decently fast but mediocrely bulky. They focus on using moves like Swords Dance to buff themselves, as their offenses tend to be around 100 range.
-Mono offense: Generally focused on one offense, they tend to be either slow and bulky or fast and weak. Mono offenses tend to focus on Physical, though Tangela is Specially oriented.
Because Grass-types tend to be slow, there isn't much of a conventional Sweeper, nor is there a conventional wall, as Grass-types tend to have low HP. Because they are overall more Defense and status spam oriented, most offensive Pokémon do not exceed around 100 range, and those that do tend to have average Speed with good defense/s.