Remove plunge so they can't jump in to pull everyone immediately. Replace plunge with unmend with 2 or 3 charges so they can poke from a distance occasionally. This also adds a different playstyle than the other tanks. Salted earth is mainly a problem because plunge can close the distance must faster than the people defending can get away. If everyone had a dancer or pictomancer dash you wouldn't see nearly as much complaining about Dark Knight as you do currently.