Ocean on bone is intended to increase the DoT damage on bone's orange skill and when runed this way ought be paired with Hydra. This build is all about the Necrotic terts btw. It is a valid rune strategy for bone and it (ocean or bolt builds for bone) see a lot of play on my main server s10. The recommended rune sets are sometimes not the ideal sets to use, but not all that often. I mean Dracul has Hail set recommended: you gotta know that's not ideal, clearly you can get more than 30 accuracy from a single minor (+36 accuracy at 5* and +12) leaving another whole set bonus available by not using Hail set.