#3 A Different Beast
Brock Lesnar has never faced adversity in his current WWE run. The last three superstars to defeat him are Roman Reigns, Goldberg, and The Undertaker. Brock Lesnar soon regained the Universal Championship he had lost to Roman Reigns.
And he also beat the tar out of Roman Reigns at WrestleMania 34 before that. Brock Lesnar avenged his loss to Goldberg by defeating him for the Universal Championship at WrestleMania 33.
The Undertaker only defeated Brock Lesnar after Lesnar had ended his WrestleMania undefeated streak, and Lesnar decisively won the feud by defeating The Undertaker inside Hell in a Cell.
If Brock Lesnar acts like he doesn't care, its because he has not been seriously challenged by anybody since returning to the WWE. His last clean loss was at Survivor Series 2016, more than 2 years ago.
So what if Brock Lesnar were to lose the WWE Universal Championship to Finn Balor? The same Finn Balor who poses the least physical threat to him. It would be one of the greatest upsets in WWE history. How would Brock Lesnar react to this humiliation?
Losing to Finn Balor would hopefully lead to a more vengeful, focused Brock Lesnar.
It is a highly compelling storyline, but Finn Balor has to defeat Brock Lesnar if the WWE is to explore it.