can also be done via command window (transportation tab) for all hubs. much faster and more comprehensive. good tip though.

Still a helpful technique and a helpful alternative by @Shades below. I was dragging a square and kept getting other vehicles involved.

This was supposed to be the easy method, because it could be a pain in the butt to find where all your little drones have wandered off too. It lets you manage the drone per-hub rather than per-drone. I haven't played in years, so I don't know how relevant it still is, but for me at the time it made a big difference doing it this way, of course if you prefer doing it the manual way, or if the game has been updated so this is less problematic, then that is fine too

Completely unnecessary. Simply select the drone or drones you wish to reassign, and right-click on the hub or controller you want them to consider home. Done.

This is also my favorite method.
BUT, there are other alternatives for different situations.
You can double click on a drone, and it selects all the drones visible on the screen. So you can control the amount of drones by zooming or moving the camera.
Pros? Much faster. Cons? Much more imprecise.
Function? Moves a lot of drones VERY fast, but PROBABLY not all of them.
I propose using the method of Lach.den.an for the scenario Vinyl presented, moving every drone at once, reliably, since you know you will catch them all.

Again, I haven't played in a long long time, so usability may have improved, but you are proposing moving ALL drones from one hub to another. If that is what you want to do then yes your suggestion probably IS easier. However, I am assuming that this guide still holds up if you want to move SOME but not ALL drones around. I specifically mentioned rebalancing the numbers, since I still wanted one or two drones left on any given hub to take care of relevant tasks, and this was (at least, at the time) the easiest way to do so. I don't THINK there was a "reassign all" button when I last played, but either way, that is for sure a handy tip for that use-case. If I end up modifying this guide, I'll try to include that point with relevant screenshots, but for now, hopefully the comments will cover that for anybody looking into it :)

It's much easier to pause the game, click the control point (this highlights the drones), click a drone, and click the "reassign all" button and click a new control point. This works on hubs AND rockets and whatever else (command rovers, I guess).

it's been just about forever since I've played, and I know there's been a ton of updates since too, I can't imagine this is something you can't do, but I am afraid I cannot answer one way or the other. Try looking in your hotkey settings, or clicking on the hubs to see if they somehow highlight their drones, or perhaps when zoomed out they will get icons over them or something. Hope you find a way!

I'd still love a way to easily find out-of-power drones that have found themselves abandoned in the middle of the landscape somehow.

What happens when I assign all to one hub? I tried to assign all in a practice game using sandbox mode, but failed utterly, and ended up doing them all one at a time. These were all drones assigned to the first and second rockets.