If only that were the case.

Surplus wind and solar are regularly wasted without grid scale storage. Often, especially in larger counties, it's not bright and sunny or windy everywhere at the same time and transferring electricity over large distances is a lossy endeavour. (If the infrastructure exists at all to carry the load - something that already prevents further renewable integration, for instance).

You also have to consider the inertia of the grid when frequency drops quickly as new loads come on line - conventional turbine generation provides (mechanical) inertia to counter this to buy time whilst new generating capacity is brought on line or shed.

Renewables such as solar and PV have no such inertia and this prevents their percentage penetration into large scale grids - although this can be remedied electronically with, once again, grid scale battery stations.

Overbuilding one system makes us vulnerable in the same way as a clone army all falls from the same infection, to borrow a terrible metaphor!