While Finishing Blow is a lovely attack, hitting for as much as 80 damage off of a Special Darkness Energy, consider Mandibuzz from Black and White. For the same number of Energy, it targets any Pokemon with some number of damage counters on it and does 50 damage to it. Now, while it requires there be damage counters, instead of Bisharp's bonus benefit, Mandibuzz can hit the Bench. Still, Mandibuzz sees very limited play.
With the upcoming reprint of Pokemon Center as an "Ability Serperior" for both players, it will be less likely for Pokemon to have damage counters on them unless they are the active and took a big hit already. For the time being, Bisharp can perform a bit more effectively than it would with healed targets. It does what it does for an Uncommon Pokemon very nicely, and has good synergy with a damage-spreader in a budget deck. For example, if it could last long enough, Forretress #13 from Undaunted could spread damage, take another Energy, and Gyro Ball to Bisharp, presuming Bisharp could take the next attack coming at it.