Actually yeah I guess you're right. Umbreon is my favorite pokemon of all time, but it only works well in competitive. In game it's even kind of difficult to go through the elite four, he doesn't die, but I set him up as a wall, so the only attack he has is faint attack, and given his crap attack stat, he's not very good in game.
Donphan, electivire, kingdra, so many others, torkoal, SALAMENCE ive never gotten my hands on a adamant/timid bagon and that sucks..
I considered using Cryogonal, but decided against it after I saw its defense stat.
Also, I've decided I don't want to use legends during my playthrough. I was quite annoyed with the ending setup in B/W, because to see what kind of stats my legend had, I had to remove one of the pokemon I'd played through most of the game with.
I really like Miltank but I wouldn't use it in competitive battling. Considering I haven't started playing in the lower tiers yet.
Ferrothorn,Tyranitar, and pretty much every pokemon in the high OUs.