I used this site to calculate the horsepower:
It said 698whp is 823hp, don’t know if it means just hp (metric (cv/ps)) or bhp.
823hp = 811bhp / 834hp = 823bhp
If it has 834hp while weighing 1419kg, power to weight ratio is 1.7kg/cv. However, if it has 823hp, power to weight ratio is 1.72kg/cv.
To compare to the Holy Trinity, the 918 Spyder Weissach Package is 1.84kg/cv (887hp, 1634kg), the LaFerrari is 1.64kg/cv (963hp, 1585kg), and the P1 is 1.62kg/cv (917hp, 1490kg).
So the 720S has a better power to weight ratio than the 918 Spyder Weissach Package, but not the P1 and LaFerrari. I’d assume in a roll race, P1 and LaFerrari win because they also have more torque, unless McLaren also underrated torque figures of the 720S.
P1 - 723lb-ft
LaFerrari - 663lb-ft
720S - 568lb-ft
The P1 and LaFerrari also have better torque to weight. But because the McLaren launch control is awesome and gets better and better, the 720S is quickest off the line. Least torque and horsepower, so least wheelspin.