It's not balance, it's continuity.
If Electabuzz evolves into Electivire, why can't I acquire an Electivire in FRLG? Simple, you just didn't find an Electrizer prior to that!
Same thing goes for Eviolite. GF really hates breaking continuity, only doing it a few times in the entire franchise - adding Steel typing to Magnemite line in gen 2, making Poison neutral versus Bug in gen 2, adding Fairy typing in XY, slight stat modifications in XY.
So now if a Pokemon gets an evolution, it would break continuity because it wouldn't receive the Eviolite boost prior to its evolution being created.
That's why you can't just evolve Eevee into Leafeon with a Leaf Stone. It was excusable in previous gens like introducing an item to make Feebas easier to evolve and introducing a special way of evolving Magneton, but there was never an item like Eviolite that limited continuity.
I personally doubt that GF actually gives a shit about Eviolite, but that is the explanation for Eviolite being involved.
>>27247288Eviolite is only good on Pokemonthat have an HP stat (ie not shuckle) and Pokemon that have recovery. Also, Little Cup.
