Espeon doesn't really have any truly favorable matchups except Korrina (even her if you miss Psybeam) and grinding happiness is inefficient for the purpose of an efficient run or a speed run. Sure it can kill Team Flare's Golbats all day but they were never really a problem anyway. It also relies on TMs, and many of the moves it wants (Dazzling Gleam/Shadow Ball) come quite late in the game. I think C-Tier is the best place for it. I don't really think any of the Eeveelutions are deserving of B-Tier. Flareon and Espeon are fine in C, and I'm still unsure whether Vaporeon and Jolteon belong in C or D.I still don't believe Espeon deserves B-tier, even if I was being overly hard on it before.
I disagree that ignoring Sylveon's method of evolution on tier placement applies to Espeon as well, mainly because it is a different method of happiness grinding and that you have a level 20 critical evolution benchmark for psybeam. If you miss that, then Espeon is useless for you until the fairy gym gives it Dazzling Gleam (or level 37 Psychic, whichever comes first). That's about three gyms of dead weight going by the NPC trainer level curve.
In it's favor, it is fast and strong and can pull the team through Korrina and Team Flare (with Dazzling Gleam for dark types), but only if you don't miss psybeam. But it still doesn't have that good of gym coverage after Korrina (heck, Jolteon has better gym coverage).