The problem with the current Sated Devourer is that it forced champions to powerfarm their jungle and being the least useful person on the map for 20 minutes and then turning into a god afterwards. It also skewed the balance on champions that used the item heavily to the point where its primary abusers had to get nerfed such that they can't live without it, the most prominent examples being Shyvanna, Xin Zhao, and Master Yi.
Bloodrazor is a much healthier alternative to Devourer in the jungle because it allows for more interaction between the jungler and the rest of the map. Your jungler no longer has an excuse for powerfarming the jungle outside of their ganks being completely awful, and allows for better balance among a lot of junglers.
That said, the idea of the phantom hit wasn't necessarily bad. It was a cool idea, but because it was ungated once you got Sated Devourer left some severe balance problems, not to mention that some champions that would normally like the idea of having the phantom hit and couldn't jungle got alienated out of the item. Having the phantom hit be the reward for stacking Guinsoo's solves both problems in addition to solving the overall cost-efficiency problem that it had before.