As for the numbers stuff, all modern air defense systems have independent integrated radar of at least their engagement range, and do not rely on external radar systems, though of course everything works much better with layering and cooperation. An F35 at max speed (which it is only capable of reach at high altitude for very brief periods of time) is hitting about 1975 km/h. An S-400's engagement and radar range is about 400km. That's an engagement radius of more than 12 minutes at max speed. The engagement window would be smaller with a low & slow approach, but then you start running into various other risks, even going back to MANPADs.
One could try a long-range stand-off but that's unlikely to prove effective without getting into the primary way to disable anti-air defenses - overwhelm them. But that's extremely non-trivial even if the systems are in relative isolation, let alone if they're part of a comprehensive anti-air system. And all of this for one system. Again I would appeal to Ukraine. Their anti-air defenses are relatively limited yet it's been more than enough to greatly limit the engagement capabilities of Russia's Su-57s.
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Actually I also completely failed to mention another major factor. If this sort of war breaks out, satellites are going boom shortly thereafter, the global internet would follow in short order. This will further reduce the chances of any sort of effective elimination of anti-air.
The Swedish air force could routinely (16% of the time) get a fighter jet based missile lock on a frigging SR-71 in the 80s! 40 years later, altitude and speed do not help as much as you think. And radars are networked.
MANPADs like the FIM-92 have an effective firing range that is a small fraction of the flight ceiling of jets, regardless of the missile's max velocity. They're not a threat unless a jet is flying very low for close air support or when lacking precision munitions, and the operator gets very lucky.