If it's just a couple of local substations, "rebooting" is AFAIK not very hard. First the substation is connected to other substations by closing the breakers on each high-voltage circuit between them, one by one; this energizes the transformers in the substation. Then the breakers to the outgoing feeders are closed one by one, which sends power to the loads. There might also be some maneuvering far from the substation to move loads from one substation to another.
What's hard is when the outage is also on the generation side; "rebooting" from a full outage (black start) can be a complex dance between starting generators, connecting substations, and energizing loads, since generation has to be matched to consumption at all times, and nearly all generators need power themselves to run (on a full black start, small diesel generators, started by even smaller batteries, are the initial point).
Remember when trying to make a vaccine was 5-10 years, but when an entire country/world makes something a priority and become hyper focused and motivated they'll 10x output.
The problem is when regardless of input you can't speed up the output. Think of a pregnancy, adding more pregnant women doesn't speed up the process, and consuming more inputs doesn't speed up the progress.
The electrical grid is nearly a "living entity". It isn't exactly like even if all the replacements magically appeared the problem is solved by a long shot.
