This is, currently, mostly regulatory. Yes, in the absence of any regulations at all it would still take time to plan, build, and commission, and I am not advocating for literally no regulations, but solar and wind plants could probably be spun up in well under a year under a dramatically reduced regulatory burden, almost certainly faster than a new Datacenter can be built. They are, after all, dramatically simpler installations.

And that's not even thinking about the fact that in this alternate reality we are imagining, power plants would have been being continually built for decades, and the new demand would be a much smaller drop in the much larger bucket.

So I think that in an alternate regulatory regime both A) yes actually power plants could built ~ as fast as data centers and other large power consumers and B) we would have so much more power that increases in demand would be less of a shock to the system.

Planning is not issue. Republican party intentionally preventimg those via goverment regulation is.