#1 Seth Rollins getting the big victory at WrestleMania

Not only is Brock Lesnar a considerably bigger draw than Braun Strowman at WrestleMania 35, but it also makes a lot more sense from a narrative perspective to have Seth Rollins, the presumed Royal Rumble winner, conquer Lesnar at the event.
For the best part of five years now, Lesnar has been booked as the big bad beast of the WWE, and very few superstars have been granted a clean victory against him, even Roman Reigns' victory at SummerSlam was somewhat tainted by Braun Strowman's presence at ringside.
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Having Rollins finally conquer The Beast at Mania secures his place as the next big star of the WWE, and also brings a much more satisfying end to Brock Lesnar's reign of dominance in the WWE.