A dedicated lead is nowhere near as effective as it was last gen, and it's sweeping abilities are sub-par, making it limited to revenge killing for offensive power. Whimsicott... I use it for support, and it really is effective. It's way too good for RU, and if smogon put it to a vote, I bet it would be banned.
Even still, a Power Herb Dactyl can wreck a lot of pokemon. I use one, but not as a lead. After i KO something with Sky Attack, i can use tailwind while the opponent revenge kills it (as it is pretty frail). i just never expected it to drop that low.