Top speed matters a lot in modern air combat, maybe more than ever. With modern fire and forget, datalinked missiles, the shooter aircraft can often immediately turn around after firing and run away from the missile coming at him. An F-15 can turn tail and run at Mach 2.5. If the AAM has a speed of Mach 4, the missile closes at Mach 1.5. Against the F-35, it’s closing at Mach 2.4. This means that the enemy’s AAMs have an effective range about 70% higher against the F-35 than the F-15. Now, this is of course dependent on being able to maintain long range tracking of the F-35, but my understanding is that against a high-end opponent, stealth is not a panacea.