DEs are still needed for the reasons that you've mentioned but in terms of importance, DTs are becoming the force.Going to slightly disagree.
Having DEs that must be accounted for helps out DTs alot. Because Sweat, Young (when healthy), and Toohill to a lesser degree, do tend to keep QB honest and not give up the edge all that often, it makes Allen, and Payne's jobs that much easier. Because neither are being consistently double and triple teamed, and when they are, the DEs are keeping these QBs honest by not giving them the edge to slip around and either run or pass for stupid yards.