You can also use coasts to cast it though, all your neighbour's rich coastal cities are open for the taking, most ships wont be able to defeat your Speakers and in SP its unlikely that the AI is going to think of using Firethrowing Golems, (never seen the AI even make one). Besides, that counter would only be available if the target player was the luchuip. Anyway, tsunami can also be used out in the open to destroy improvements and do serious damage to units outside of cities. A good extra to this strategy would be a waterwalking Hemah casting air elemental. I never tried this in my game (as lanun), but air elemenals spawning lightning elementals should be able to finish up a lot of damaged units. I'm going to try a new, similiar game a.s.a.p to test this strat properly.
The strategy should work with any OO civ although the Lanun have the most to gain (better use of coastal cities) then most other civs. Falamar would be better for getting Speakers quicker. A civ with the Spiritual trait would be good too as most of your army is made up of disciple units. Unfortunately the only one wo comes to mind atm is Os-Gabella, who has much better synergies with AV.