We're talking about nation-state on nation-state hacking here. The kind of investment you're talking about would have to be absolutely massive, and even then it still might not do the job.

And even if that kind of investment in cyber-warfare/security capabilities is undertaken, the military isn't going to stop "dumping the money in machines designed to carry meat-bags" until after it's very clear the investment was successful. It's not realistic for a first rate to take the kind of risk you're talking about if it wants to remain first rate.

And if that's a realized threat, the planes can be disconnected and still function at a reduced capacity. That's not true for drones.

It's like GPS. It's a really nice technology, but warplanes and weapons also have IMUs, so they'll still be effective if GPS has been jammed/knocked out.

Most horses were used for logistics if I recall.