That method works well for Z wave, but it’s not always the best approach for zigbee because of the hard limit on the number of children that the hub can accept.
By having everything turned off except a single tier you pretty much force devices to try to choose the hub as a parent. And when they do that, the hub’s child slots fill up much sooner than if you had all the devices turned on.
As far as the OP’s problem, it does sound likely that some repeater somewhere, or maybe a couple of them, was either damaged by the power surges or just didn’t come online and that ended up with its perspective children trying to find other parents which then can block other child devices from finding a parent and all that.
It also sounds like the only repeaters they have are their IKEA bulbs. These are good repeaters, but only if they are on power. So my first question would be were all the bulbs on power at the point that you started trying to add things back?
Not being able to add a device is very frequently because you’ve reached the child limit somewhere. See the following FAQ:
FAQ: 32 Zigbee direct connection device limit?
So speaking as a former field tech, what I would do, is take the hub off power (including removing any batteries) and leave it off power for 20 minutes.
Meanwhile, go around the house and make sure that every single other Zigbee device is on power, including the IKEA bulbs. This is what will force them all into panic mode because the coordinator is off-line and will cause everybody To find new parents once the hub does come back online.
Once you put the hub back online, it may take a little while for everything to sort itself out. Maybe even a day. So just make sure everything stays on power during that time. The lights can be turned off from the app, just make sure they still have current.
Then see where you are the next day.
But the building out from the middle method works well for Z wave networks. Just not well for Zigbee networks. For example, suppose your hub is in your living room on the first floor. There are two zigbee pocketsockets on the floor above. Or in this case maybe two IKEA bulbs.
If you start building out in waves, you might start adding child devices that are along the first floor hallway, and they might be forced to attach to the hub as the only available parent. Where previously they would’ve used the IKEA bulbs on the floor above as a parent. This in turn might mean that the hub starts refusing to add additional child devices before you ever get around to turning the IKEA bulbs back on.
Anyway, zigbee is pretty good at self healing, but I would make as many repeaters available at once as possible, just in case the most effective network setup is to bounce out before coming back in.