Necessary - not at all.
Races are still being won on bikes equipped with either brake system.
The day only disc bikes win races it’ll be b/c all riders capable of winning are on disc bikes. Presumably more by sponsorship deals, upgradeitis or sheer availability rather than any huge performance advantage.
How NICE and/or BENEFICIAL discs are vary from rider to rider.
And ever from ride to ride.
While I rode for decades with rim brakes with nothing more than some mild grumbling during wet rides and when a rim wore out, I sure appreciate that discs require less hand effort to give the same amount of braking.
Not having to wait a full turn of the wheel or two before getting good braking in the wet is also nice, particularly in tight situations.