[del]What Eevee deck are you playing?[/del]EDIT: Oh... See the bottom for my thoughts on that kind of Eevee-lution <_<"
Original post:
I tried out Glaceon and... Pretty much it (Espeon and Umbreon, but meh, those don't count) and I noticed three problems.
1) Lack of reliable recovery from KOs
2) Low enough HP to be Two-shot by everything (Garde has this as well, but is much easier to do recovery with)
3) Underwhelming damage (again, Garde has same problem, but is MUCH easier to support, especially since its power lock ISN'T broken by Warp Point)
...Leafeon might be able to answer all of those questions. Simply swarm with Leafeon #7 and only play one Leafeon LV.X, then flood energy onto everything fairly evenly and deal damage with Leafeons rather then the X. Your recovery is a lot safer since everything has energy as opposed to only a LV.X who you NEED out. The HP's fairly high on Leafeons, particularly on the LV.X whom has enough that Garde isn't going to two hit KO it (with Espeon, of course). OBVIOUSLY Leafeon LV.X has a HUGE damage potential, so three doesn't apply either.
...Running EVERY Eevee-lution though just asks for trouble, me thinks. Glaceon deck alone had enough trouble trying to allocate Eevees to evolve, and that's ONLY with Glaceon, Espeon, and Umbreon
But Leafeon... Maybe that has the ability to fill in the gaps that Glaceon leaves, though Glaceon is probably the single coolest card in the set [del]I love Garchomp more, but couldn't resist the pun ;_;[/del]