You are confusing the grid with generation capacity. They are different. Generation capacity is where we have more need. For the most part the wires have enough capacity - though even then there are places that need upgrades.
I have a few reasons to believe the wires we have today aren't enough
1) I was recently talking with someone who lives in a community where homes have 60A service. The homes and last mile in places like that can't handle the draw people will need to electrify everything. 60A isn't enough.
2) Where I live there has been work to upgrade the wiring because it's not enough. It's not done yet and other communities I've been to have not been upgraded, yet. There are still areas where the current traveling through the lines today causes enough sag that I wait for something to break when things are at their peak.
3) Publications and communications from some power companies cover the need to upgrade the grid. Are they lying?
