“everyone can plug in at the same time, the cars will simply charge at the rate the grid can handle.”
No, that’s not the way electrical grids work.
Firstly, grids dont discriminate between “car” and “your employers computer system”. If demand exceeds supply instantaneously by 30% that’s a general brownout where most electrical goods don’t work.
And secondly, that’s *really* not the way grids work.
Grids target 50Hz frequency as the way to maintain exact balance between supply and demand. If the frequency drops past 49.5Hz limit ( 1%) , they drop entire sections of the grid off completely until balance is regained. Once a section has been dropped, it takes between ten minutes and an hour to re-stabilise and reconnect. Can you see the problem?