Modern fighters are moving towards a sustained supersonic speed through supercruise as opposed to short bursts of Mach 2 speeds seen in second/third gen aircraft.
The most successful Mach 2+ aircraft have been surveillance and reconnaissance aircraft. The ability to quickly cover large distances at 70000 ft was invaluable in the past. Today, with systems like S-400 things have changed.
That said, armed with precision air to ground weapons, the ability to perform a Mach 2+ pass in low level flight to drop ammo and scramble out of the hot zone would be valuable. Taking things a bit higher in the air, the number of kilotons/megatons of nuclear payload that can be SAFELY dropped by a plane is bounded above by the max speed. Certainly, a short Mach 2+ burst immediately after releasing a bad boy would be highly appreciated.
Yes, you can't outrun a Mach 3.0 missile at Mach 2, but the missile doesn't have long legs. At a certain distance, Mach 2.0 would increase survivability because the missile would fizzle out.
Yes, you can't make sharp turns at Mach 2, but even a 5 degree turn would take you very far in a very short time. If someone is crazy enough to do hot pursuit at Mach 2 they need to blink an eye and you would be gone.
In the end, every capability opens up the possibility of different tactics, each with its own pros and cons. It is the tactics that matter. If our tactics require Mach 2, the thunder will have it. If a customer's tactics require Mach 2, we would need to develop it for them.
