You ignore the same problems with air platforms emitting.
Your claim about detecting the data link is absurd.
Even point to point microwave links can be detected off-axis.
Hundreds of watts of point-to-point means dozens of watts of sidelobes.
Dozens of watts in the middle of the desert is easy to detect.
If the AN/MLQ-40 could do it at tens of kilometers 20 years ago I bet datalinks could be detected from space today.
What part are you confused about?
There is no such thing as a perfectly directional antenna. Radiation profiles consist of multiple lobes which generally point towards a single direction on 3 axes, but there are always side lobes, like so: [1]. You can't hide these, therefore they can be detected and targeted.
There's a whole class of missiles that simply look for RF sources and head that way. The only way to avoid such missiles is to stop being an RF source. But if you do that, you're also unable to target the attackers or defend against those missiles. You also have to turn off your data link and lose situational awareness.
The S-400 is the best air defence currently fielded, but it is by no means magical or invulnerable.
https://www.cisco.com/c/dam/en/us/products/collateral/wirele...
You don't think the s400 has any jamming capability and protection of its own? You don't think the system can detect when it's being targeted and locked on?
It can definitely be defeated but not without suffering heavy casualties. That's _why_ it's called anti-access/area denial technology.