>>36738264They need almost the whole package. First a little revamp of their stats, since they were supposed to be reliable mons on their speciality. You could do that by increasing their two better stats in 15 points each, for example, and balance the rest of them to avoid making every Eeveelution either fast and frail or bulky and unable to harm anything in OU
Second, they need new Abilities. Vaporeon, Jolteon, Flareon and Umbreon are still using their original Abilities. Glaceon and Leafeon use their Hidden Abilities, but those are related to the two worst weather conditions. Only Espeon and Sylveon have good and consistent Abilities. I am talking about the likes of Drought or Terrain-related ones, since that would help spread them around the tier and not make it the Tapu fest it is nowadays. Sheer force (as an upgrade from Adaptability, Eevee's second Ability) or -ate Abilities could make a good choice too, but they wouldn't be probably enough to make the jump to OU.
Lastly, they would need a wider movepool, both in the offensive and supporting roles. It's painful to see only Sylveon and Espeon have a wider range of options in Dazzling Gleam, Psyshock and Grass Knot. And still they lack something to hit steel types, appart from Hidden Power. So, for starting, I would give Eevee both Nasty Plot and Sword Dance (if the latter is not already learned by it). Letting Eevee keep its special moves from Let's Go would be an interesting option, but I understand that's not possible. But you could give them moves of the different Eevee types with a not-so-high BP, like Flamethrower or Energy Ball. Finally some utility moves according to their flavour. In this area I have always thought Jolteon could make for a decent user of Spikes/Toxic Spikes.
>>36738479All of them at the same time could be too much. But different combinations of two or three, like an Eevee Soul Dew could be fun
