But the jammer can be plugged in to the grid or a diesel generator. Being on the ground without flight requirements grants access to such resources.

True, but they can't use directional antennas nor lots of power, and once they're far enough from the transmitter inverse square law does the rest. Ground stations always have an advantage because of higher gain antennas and more power available.

I mean, drones trailing fiber optic cables are widely documented https://en.wikipedia.org/wiki/Fiber_optic_drone

So I’m pretty sure avoiding jamming by a military adversary is not trivial, even with frequency hopping and suchlike.

So what? It's not the airborne platform with limited energy and an explosive payload that needs to do the jamming, it's the ground-based targets.

However, as pointed out elsewhere in the thread a lot of these jamming arguments are academic because drones are either tethered with a fiberoptic cable and/or navigating autonomously.