GF spoiling that fire lizard and electric mouse with with new gimmicks and signature moves but constantly ignoring my umbreon.
Seriously atleast give it poison heal as ability and parting shot and topsy turvy as new moves.
I actually agree with this. Eeveelutions used to be good, but as Gens passed, and more Mons appeared, they slowly became totally outclassed, since GF almost fully refused to give them new moves.
Typing, Stats, Abilities and Movepool. This are the 4 factors that decide whether a Mon is good or not. How to improve the Eevees with these 4 factors in mind?
Typing: No. This one is impossible to do, since one of the defining characteristics of Eeveelutions is being pure type.
Stats: Again, pretty unlike to change. There is a small chance though, that one of the 65 Stats (each Eevee has 2 of them) could be increased. Still, said increase would be 20 points at most, so the viability doesn't change much.
Abilities: Now, this is where the fun begins. What ability could each Eevee have that at the same time would make sense?
Vaporeon: Poison Heal fits here, Vaporeon learns Acid Armor and some poisons are liquid. Regenerator would also work, Vaporeon already heals with water or rain. The ability to replace would be Hydration.
Jolteon: Quick Feet for this one never made sense and never helped. Rough Skin doesn't help too much on offensive Mon either, but it's still better than Quick Feet. Drizzle is too much of a stretch,but would help to abuse Weather Ball. Another idea, given the pathetic offensive Movepool of Jolteon, would be making a new ability just for him that allowed hitting Ground types with electric moves. Jolteon is not strong enough to break the game with that, but would jump up many Tiers.
Flareon: This one is hard. It's slow and frail at the same time, so something truly broken is needed. Contrary is an ability that has a very random distribution, so Flareon could use it well with Superpower + Overheat (or even some new move).
Espeon: This one is good enough in this aspect, nothing needs to be changed.
Umbreon: Shadow Tag fits, but it would be broken, just like Gothi. Poison Heal fits too, since Umbreon was originally designed as a Poison type. However, the best option for me is Magic Bounce: Umbreon already shares one ability with Espeon, why not make them 2? I really wish some non-psychic Magic Bounce user to exist now that Mega Diancie, Sableye and Absol don't exist anymore.
Leafeon: Natural Cure fits here. Another option is making Leaf Guard an Hydration clone. Neither of these options improve Leafeon much. The best solution for me would be making an ability similar to Cherrim's one, that increased Attack and Speed 50% when in Sun.
Glaceon: His strange eyes could make a case for Tinted Lens. Those Steels and Fires don't wall that 130 Special Attacks anymore.
Sylveon: Like Espeon, nothing to change here.
Movepool: This is what has most options, but also the hardest one to decide.
Vaporeon: Some offensive poison moves would make Poison Heal fit more, though in practice they don't help Vaporeon too much. Well, if Vaporeon has Poison Heal, it doesn't need much more, that ability is really good.
Jolteon: Spikes are obvious, even without new ability. After that, it gets trickier. I guess Calm Mind could work, doesn't it get that in PLA?
Flareon: Sacred Fire (after all, a Flareon died and was transformed in Entei by Ho-oh, both of those know the move) could be a move to have. Slack Off is there too for a slow and lazy Mon. V Create is of course very crazy, but it sounds similarly to eeVee Create, so for me that's enough of an excuse and it helps to the Contrary cause.
Espeon: Why does Sylveon get Mystical Fire, but not Espeon? After that I really don't know what to do, besides crazy exclusive shit like Psystrike or Photon Geyser. Maybe Parting Shot?
Umbreon: Now, this one fits for Parting Shot. Also for Roar, many Eeveelutions get Roar, but not the one that would take the most advantage of it. Knock Off never hurts to have, though thats a move I would like to have a smaller distribution, and Umbreon doesn't really fit.
Leafeon: Close Combat fits here. Leafeon attacks with her ears, but uses them well.
Glaceon: It evolves by being close to an Icy ROCK: good excuse for Ancient Power and Power Gem. It learns Mud Slap, so Earth Power time!
Sylveon: It attacks with sound move Hyper Voice most of the time. Upgrading that to Boomburst isn't hard. Oh, and Earth Power would also help, though doesn't really fit.
Most of these will never come true, but hopefully actual Eeveelutions improvements come in Gen 9.