And Mach Punch is also STAB to Ropushin. But as others have said, Mach Punch is resisted Priority which is the point of what ungulateman said.
Ah so you don't have a point.
Anyway Espeon is obviously an incredibly useful pokemon for Offensive / Balanced teams that previously may have struggled with status / entry hazards / phasing, which a lot of them did.. EspyJump is probably the set with the most utility once Espeon's switched in and reflected the status move. It's up on the analysis site, but for those who don't know it's essentially just a Substitutue Baton Passer that typically trades power for bulk.
However it seems if Espeon is to become effective in OU I believe it may have to adopt a more attacking perspective so it is not rendered useless by threats such as Scizor or Tyranitar. Im thinking something like:
Espeon @ Leftovers
~Substitute
~Baton Pass
~Psycho Shock / Psychic
~Grass Knot / HP Fire
Timid
Magic Mirror
4 HP / 252 SpA / 252 Spe
Under Sandstorm Grass Knot does 51.5% - 60.8%, an impressive 2HKO, to 4 HP Tyranitar and heavy damage to Suicune and Hippowdon, whereas HP fire OHKO's Scizor, Forretress and Nattorei so the choice is dependant on your team. Psycho Shock may be rendered pointless however, it only does 33.2% - 39.2% to WishBliss which is the main target, and it will do even less to Pre-Evo Chansey. Psychic should probably be considered for its ability to OHKO most Roobushin, something which Psycho Shock cannot do.