One of the main benefits of a DDI is removing conflict points - yes, traffic slows in some cases, but if you study that diagram, you’ll see that it eliminates all instances of traffic needing to turn across opposing traffic…research shows that this is where many of the most severte/fatal crashes tend to happen.
Another one you’ll see increasingly used in coming years is a single-point urban interchange (SPUI). Like the DDI, there are significant safety benefits, in addition to not consuming nearly as much land adjacent to the highway.
Edit: also, not sure what you mean by “death circle”…roundabouts a far and away safer than traditional signalized and two-way stop controlled intersections…in many cases, they can also be safer than four-way stop controlled intersections, because drivers are physically forced to slow down instead of just having to obey a sign. In a very few cases, more crashes may result, but these tend to be low-speed, property damage only crashes, not fatal or serious injury ones. My job (as a transportation engineer and professor) is to help reduce blood on the pavement, not plastic.