Cummins to go to No. 1 in the rankings and stay there for years
Root to slip out of the top 10 and no longer be discussed with Kohli, Smith and Williamson.
That's not really surprising when you look at the stats in depth
On Western pitches (South Africa, Australia, New Zealand, England):
Cummins has 76 wickets @ 21.14, SR 42.07 in 15 test matches on western pitches.
Rabada has 158 wickets @ 22.25, SR 39.92 in 30 test matches on western pitches.
Steyn has 318 wickets @ 22.97, SR 42.62 in 65 test matches on western pitches.
Cummins appears to be a better bowler away from home vs Rabada though (Small sample size) and Rabada has the advantaging of bowling on South African vs Australian pitches for the majority of his wickets.
Cummins has barely played a minnow yet either, Bangladesh (Away) probably isn't too applicable, 90% of his matches have been played against South Africa, India & England. With both of them being played away.
His first real match against a smaller test team in favorable conditions was on the weekend and he absolutely destroyed them with 10/62.