An evolution for Jynx to complete the "set" of Electabuzz, Magmar, and Jynx that was never finished.
But they aren't a trio.
What they have in common:
-got a pre-evolution in GS
-said pre-evolutions evolve at Lv30
-each learn one of the elemental punches
-they've been close in the pokedex most of the time..
But now look at the list of things Magmar and Electabuzz (who are indisputably counterparts/a duo) do have in common but don't with Jynx:
-pure elemental energy-generating types. Jynx has the cold elemental type as well as being a dual type with a Psychic on top of Ice.
-mostly male gender ratio (75/25). Jynx is exclusively female.
-very close total base stats(360/365->490/495). Smoochum/Jynx have ~50 less total base stats (305->455), meaning it's not even meant to be the same "level" of Pokémon. That makes Jynx to Electabuzz/Magmar what the Hitmons are to Machamp in terms of stats..
-even the closer stat distribution, in Electabuzz and Magmars case, their highests stats are both Attacks, followed by a moderate speed, whereas Jynx is clearly laid out as a fast special sweeper only.
-both have the Hidden ability Vital Spirit (cannot sleep because they're so energetic), whereas Jynx has a random Dry Skin since the energetic theme is absent.
-always consistently version exclusive. Jynx however is never factored into that and is obtained by some other manner or not at all, regardless of version differences.
But the most glaring difference is in the designs themselves.
Here you have 2 clearly animal-based designs (cat and duck?) with an increasingly humanoid look.
They are also blatantly covered by the elemental patterns that make it impossible to miss their types. You cannot make Pokemon designs scream "Electric" and "Fire" more clearly than these.
Jynx on the other hand...
For a third member, you'd expect a pure Ice type monkey/bear/whatever animal-based design, that's covered in an icy pattern.
So...I have no problem with anyone who wants an evolution for Jynx in general. But "to finish the set", what set? o_o
tl;dr
the differences between Jynx and Electabuzz/Magmar far outweighed the similarities, even before gen 4 completely closed the case.