Aside from "Mythical 1, 2, 3" I don't see a problem with the Archetypes. I mean I guess the Pikclone is probably next, but recent ones tend to follow another Archetype (Standalone Flying, Fairy, Steel, Dark) (Emolga, Dedenne, Togedemaru, Morpeko respectively)
The problem is not so much the archetypes themselves. It's rather the fact that they insist on keeping nearly all of them in every generation, even as the total number of Pokémon shrinks. That leaves way less room for non-archetype representation of certain types, and it makes three-stage families extremely rare, apart from the somewhat repetitive archetypes. I mean, when was the last time we saw a three-stage Flying-type family that wasn't a bird encountered on the first two Routes of the game and didn't evolve twice by level-up, around levels 14-20 and 30-36? Actually, let me look that up ...
...
... yeah, that was the Hoppip family. Or the Zubat family, if you disregard the "bird" requirement. Literally all the other families that are Flying-type in all three stages have been regional birds.
Other types have the same problem. Fire and Water are both automatically represented by a three-stage family by way of the starters in every game, so non-starter three-stage families of those types are unreasonably rare. The Rolycoly family is one of only three three-stage Fire-types that aren't starters (alongside the Magmar and Litwick families). The Tympole family was the last non-starter Water-type three-stage family. Bug has only seen
one three-stage family cast in a different role than "regional bug", and that's either the Venipede or Sewaddle family depending on which one you consider the regional bug in Unova.
Archetypes aren't bad per se, and there is a lot of wiggle room for creative design within the limitations they represent ... but they still represent limitations. Game Freak likes to create Pokémon that follow the same basic patterns in every game, and that is fine, provided that they create some Pokémon
outside the patterns as well. And for a large number of types, this is done only very rarely, at least for three-stage families.
And to try to twist this rant back into something appropriate for the thread, let me explain why I focus so much on three-stage families. In short, it's because they are a little thing I really like.
A two-stage evolution family features a basic Pokémon and an evolved form that looks a little bigger and tougher, but generally follows the same basic principle. Little horse evolves into big horse. Little bug into big bug. Bud into flower, that sort of things. The first and second stages have to look somewhat like each other to make the transition believable and not too abrupt.
However, a three-stage family can begin with an extra small and cutesy creature, and end up with an extra big badass as the final form. The second stage creates an effective middle step between the two, making a gradual and believable transition from little guy to big guy. This way, there can be a bigger gap in the design between the first and final evolution steps. That means the first stage can go even further in the direction of small and cutesy, while the third stage can go further in the direction of elaborate and badass. Just look at, say, Swinub and Mamoswine or Rookidee and Corviknight. Without the respective middle stages, you wouldn't guess the first and final stages were related. But the transition looks believable because of the middle step that bridges the two. It gives the Pokémon family a much wider span on the basic - elaborate scale.
The same can be said about gameplay. Two-stage Pokémon you find in the early-game tend to evolve into a creature that loses its relative strength by the mid-game or so. The power level doesn't increase much in the span of one evolution, so Pokémon that evolve early become obsolete early. Likewise, two-stage Pokémon that evolve into something with endgame stats tend to appear only late in the mid-game, at which point you may have settled on your final team already. Pokémon like Noibat or Mienfoo debut too late (in their original games) to be attractive to catch. And if later games introduce them as early-game Pokémon, they will only serve as useless baggage for the entire mid-game until they finally evolve on Victory Road or so.
However, a three-stage Pokémon can be a weak Pokémon in the early-game, a serviceable Pokémon in the mid-game, and a strong Pokémon in the late-game, all in one. No need for them to be discarded halfway through your adventure, or to appear so late they become uninteresting. You can catch it outside the first Gym, evolve it in time for the third Gym, evolve it again after the seventh Gym, and take the final form to the Pokémon League. It has a role to play throughout the entire game.
In short, three-stage families span much wider, both in terms of appearance and gameplay utility, and they are (usually - hello Dreepy!) very flexible for appearance in later games as well. That's why I tend to use them as much as possible, and why I think it's so sad that they almost aren't making them anymore.