Agreed.
From the moment it hits the field, Kingdra will get at most one free turn to boost with (the turn which the opponent uses to swap in their counter). No competent player will sit on their hands and let a Kingdra use Focus Energy and Agility. They'll either OHKO it on Agility, or weaken it to the point where a strong priority move will finish it off.
Your best bet at getting Kingdra to +2 Spe with Focus Energy is to Baton Pass the +2 Spe from a Scolipede (Scoli's a magnet for Fire-type attacks). Kingdra takes practically no damage thanks to a 4x resist, and forces a switch; the "one free turn" it needs to set up Focus Energy. From there, Kingdra outspeeds all of OU minus Scarfers and can spam Draco Meteor or Hydro Pump (which can 2HKO standard Ferrothorn).