The UAVs are operated by humans with downlink. Trained operators, maybe even pilots, perhaps with much SAR experience but sitting in an environment with a bigger capacity seat than a helicopter.
The technology has been used to search for humans for a while now, difference being most of them didn’t want to be found because they ended up getting lifted or waxed.
I'm not dismissing the operator training, nor the fact that you can detect people with the technology - I mentioned earlier that I did the first RAF SAR job with the FLIR systems turret and have been repeatedly impressed by its capability.
My point is that with one sensor on a UAV (FLIR/TV turret I am surmising), you are only able to search what the camera can see (whether in autoscan or manual) and, just like a helicopter, the height and speed will have to be adjusted (along with the track spacing) to match the conditions to what you are searching for.
The flexibility of a helicopter vs a UAV is the ability to slow down and go down to investigate possible sightings - a regular part of any search - all the technology and operator training won't match that
A well trained person in a comfy chair miles from the scene will never be as effective as the same person in a helicopter cockpit or cabin actually on scene.
But someone will see a shiny toy and potential cost savings, buy it and then leave it in the hangar because it can't do what is promised.