We can look it in two ways, batter has the advantage only if the wicket is flat, anything else, say swing, seam, spin, slowness, bounce, low bounce, goes in favour of the bowlers. Now with saliva, reverse also comes into equation (even on flat tracks)
Bowlers who've been great bowlers were/are great because they were/are also master of their art even on flat tracks, vice versa, batters who've been great batters were/are great because they were/are masters of their art even on not so flat tracks
Even in this IPL, with all the huge scores, one particular bowler each innings has an economy less than the innings run rate, what did those bowlers do different?