AFAIK there has not been a conflict since WWII that we did not enjoy air superiority over every inch of the theatre. Until now. Read up on Russia’s air defense. The CIA has made it’s last stupid mistake.
To be fair as to your point about Russian air defenses our military has made the mission a top priority with dedicated wild weasels and jamming aircraft. The F-35 appears to have some value with its stealth capability at reaching radars safely and they are supposedly bringing back the F-117 and I suspect it might be for this purpose as well.
The Israelis have a fair amount of experience penetrating and testing Russian radar systems with the F-35 and I suspect they are sharing much of what they have learned. Static defenses (like the S-400) are also very vulnerable to stealthy drones.