That's too strong an assumption. The USAF 's bread and butter is supersonic stealth jets that can enter a territory, fire RF missiles to take out anti-aircraft radar, and leave faster than anything can catch it. Repeated hit and run attacks that wear down ground defenses until they can fly unchallenged. That's on top of the massive arsenal of precision guided missiles that will take out any static installation identified by constant global satellite surveillance.
NATO doctrine has always been geared towards countering the Sovet Union/Russia, despite the counter-terrorism detour the US took.
Even MANPADs, which are extremely cheap (relative to an aircraft) pose a major threat. For instance the now somewhat dated FIM-92 [2] can hit mach 2.2. This is why even though Ukraine's air defenses are overall somewhat limited, Russian aircraft rarely if ever go for deep missions. Air superiority is probably just impossible in modern times against a peer adversary.
[1] - https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird
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.
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.
It is unclear if the US will prevail against a peer adversary in an air war, but if anybody is able to achieve air supremacy, it would be the US and their allies.
F-35 can't super-sonic cruise. The choice was to be slow but stealthy.
And that's not counting the rest of NATO.
I would not say that they will succeed in a peer to peer war, but NATO have the greatest chance to achieve air supremacy against any peer opponent.