Weirdly, it's actual black magic - the regular Marathons have the lowest rolling resistance of any touring tyre[0](lower than Schwalbe's own Marathon Racer lol), despite being very good at puncture proofing and not being completely slick. No idea how Schwalbe has actually done it.
[0] https://www.bicyclerollingresistance.com/tour-reviews/schwal...
You can't really win, the stiffer the tire the better it is at protecting the tube but the rolling resistance is higher and the tire flexes less which makes it less grippy.