Compare Dupont Circle to Connecticut & K st. Down at K & Conn. they need to use at least 5 traffic officers to direct the flow during peak times.
Meanwhile Dupont circle handles P street, 19th street, Connecticut avenue, Massachusetts avenue, and New Hampshire avenue. Plus there is the pedestrian traffic from the park and the metro stop at Dupont.
Can you imagine doing that with only traffic lights? How many officers would be required to massage that mess?
Unless you propose building a spaghetti mixer, I can't imagine a better system for drivers or pedestrians.
New York and Chicago manage to handle streets just as busy with regular 4-way intersections. The problem with any K street intersection is the bizarre access roads on each side that confuse drivers to ill effect.
Yes, the roundabouts here in D.C. long ago outlived their usefulness. Unfortunately, ripping them out probably isn't in the cards.