Wasim Akram was better than Dale Steyn by lightyears.
In both formats.
Wasim Akram was so dominant and fierce a fast bowler in the limited overs format that no fast bowler in the history of the game approaches him in terms of talent, variation, performance, ability or record.
In Test matches, Dale Steyn is about 20% inferior, on average.
Wasim bhai had more variety, more control, greater performance, better records, poorer fieldsmen dropping catches one after the other while Dale Steyn or other Saffies had some of the best fielding units in the world helping them boost their averages and other stats in bowling friendly saffer conditions.
On top of that, there are numerous obvious cases some of which you can find videos of even today where Wasim bhai and Team Pakistan was blatantly robbed of Test victories abroad, two prominent cases being the Hobart test where Justin Langer was caught behind and the Antigue Test where Jimmy Adams was caught behind, but the umpires either cheated or made terrible decisions that cost Pakistan the games, and Wasim bhai's stats also suffered accordingly.
In both ODIs and Tests, there are dozens of such examples where let alone umpires, the nonstriker had a hard time figuring out the late swing or deviation or some other mesmerizing variation of his delivery that Wasim bhai would come up with.
Stats wise, Wasim Bhai is at least 20% better than Steyn in Tests. No contest in ODIs as Wasim Bhai is the best ever ODI bowler by quite some margin.
FYI, Wasim Bhai averages 24.28 despite all those dropped catches, denied LBWs, denied caught behinds, conflicts in the dressing room and all that - against Top 8 sides, away from home.
243 wickets, at 24.28, with 16 5Ws, in 58 Matches, 103 innings. Econ rate of 2.59, 11 MoM, 5MoS.
Against the Top 8 sides, away from home, Dale Steyn despite benefitting from the superior Saffer fielding unit and emergence of much poorer batting techniques and temperament around the world due to T20 influence, averages 26.09.
147 wickets, at 26.09 with 9 5Ws, in 33 Matches, 59 Innings. Econ rate of 3.36, 3 MoM, 1MoS
Even in his supposedly favoured format of Test cricket, Dale Steyn still comes up short by a significant margin by all available indicators. In terms of stats. And in terms of ability, talent, imposing presence, ability to toy with the best and most technically correct and/or aesthetically pleasing batsmen.
Wasim Bhai wins it comfortably in all formats, Statistically, in terms of ability, control, match winning performance, variation, records, and you name it.