The combo system changes are more aesthetic than anything else. In 3.x, you make a decision on each combo to either use DASE or Delirium, depending on your MP level. SE is never used without DA, so the base ability is kind of useless.

In 4.x, the SE combo without DA is the old Delirium combo, without the INT down effect. You have less variety with the animations, but you're functionally doing the exact same thing. You also make decisions about DA use at multiple points in the combo to ensure that you don't cap. You have the opposite problem to HW: you're not going to lose dps when you bottom out on MP, you're going to lose dps when you cap.

This would be a better change if it wasn't for the fact that the lifesteal effect of SE was locked behind Grit, as Souleater has more use. At the moment, the main drawback is that it forces more double weaving. The time interval between SE and SS becomes that much more handy for setting up DA oGCDs, as a result.