Wildly dependent on your definition of "modern", which mostly depends on your potential adversary. The Russia/Ukraine, and the new war in the Gulf have shown numerous ways in which 4th generation jets, and more importantly cheaper missiles and even more cheap drones can perform supression of enemy air defences and/or air support. Unless you're fighting the US or China, 4th gen jets are plenty. And even against US and US defended locations, cheap drones and missiles have been able to influct some pretty serious damage to critical infrastructure (like extremely expensive and rare radar systems). An adversary not crippled by extreme sanctions and corruption for decades might have been able to achieve even more, even with the total lack of airpower.
The real reason stealth is needed is as a counter to GBAD. Modern anti-aircraft missiles are incredible lethal.
But isn't that true of the F35 as well?
On it's own, I doubt it would survive much longer on the eastern front in Ukraine.
In Iran the F-35 also did not fly around freely while the ground radars were active. They had to be taken out first. For that stealth was probably useful (and in general it is).
But it is not making them invisible - and cheap sensors and AI is likely to counter it soon. Because sensors and analysis will get better over time and sensors also better and cheaper. But the stealth will remain largely the same. It cannot really be upgraded for existing jets.
> have no choice
That's my point. Any battlefield today is "modern", but militaries operate with what they have. From Russia to the Houthis passing via the Houthis, we've seen insane amounts of damage done on "a modern battlefield" with anything from Cold War era equipment to cheap drones assembled by a terrorist group living in the mountains with no industrial base.
Yes, if the US wants to fight China, and vice versa, it needs 5th gen jets. Everyone else doesn't need them. They're nice to have to make your job easier (like Israel vs Iran), but don't guarantee you anything (like Israel vs Iran).
It's quite likely that in about 5 years most military installations will have a mix of weapons to intercept those systems - and depending on a number of factors you could easily end up back at low performance drones being so reliably intercepted as to be a waste of munitions to deploy.
WW1 after all was based on exactly this thinking: surely the volume of an army would overcome the machine gun.
That's unlikely. Anti-drone defences will only improve, yes, but autonomous drone swarms numbering in the thousands to tens of thousands are doable today, and few weapons systems can handle the rate of launch/fire required to combat that. Especially if there are follow-up waves mixing drones and heavy missiles against which your anti-drone defences wouldn't be enough.
> WW1 after all was based on exactly this thinking: surely the volume of an army would overcome the machine gun.
But building a cheap kamikaze drone costs much less than building a human.
Autonomous flight control software is still only able to handle the simplest missions. Maybe that will change in a few years but for now anything complex requires a remote pilot, and those communication links are very vulnerable.
Torpedo boats didn't make Battleships obsolete. Aircraft carriers did. Because they could do the same role but better.
AntiTank rifles didn't make tanks obsolete. Neither did anti-tank mines. Nor anti-tank rocket launchers, nor anti-tank artillery, nor really freaking good anti-tank missiles, nor anti-tank helicopters etc etc. Turns out, putting a box of steel around soldiers is pretty much always better. IFVs are even less survivable than a tank in all cases and they have only become more important and prominent because what capability they provide is what matters.
Artillery and Air power did not make the army obsolete. Air power did not make Artillery obsolete though the USA wanted that reality.
Submarines didn't make any boat obsolete.
SAM systems did not make planes obsolete. Hell, America decided the solution to missiles aimed at your planes was fly planes at the missile launcher! And it works because war is stupid.
"Cheap drones" only work against things that haven't yet adapted to cheap drones in the exact same way that Navy had to adapt to anti-ship missiles. With EW, those "cheap" drones get less cheap. With any sort of advancement in protection, those drones get less cheap. War is about achieving physical control, and you can't really do that with cheap drones. There's always back and forth in weapons systems. We still use bayonets in the right circumstances!
Cheap drones cannot establish air superiority, and certainly not air supremacy. Actual air combat drones are far more expensive, involved, and in development than quadcopters.
The primary power drones bring is ISR, making the entire battlefield utterly transparent, including at nighttime. That's insane, and really really bad for any of us who might be forced to fight in the future, as lethality to the average soldier is likely to go up.
