"Uneven electricity output"?

The variation on output is over a matter of hours (wind powerful enough to spin entire wind farms is not something that comes one second and is gone the next), and large grids with import and export capabilities are largely self-regulating.

Cost fluctuations in the electricity market regulate whether e.g., power storage sites will charge or dump power, whether district heating plants will source more heat from giant electric kettles, when EVs will start to charge, when private smart water heaters will preheat, when people decide to schedule washing machines and dishwasher, whether offline fossil fuel power plants will be fired up to sell as the rate becomes more lucrative or shut down as power becomes too cheap, whether any "idle" plants will throttle up or down, and whether windmills will engage brakes and turn away from the wind or release brakes and turn into it.

Power grids have also always had the ability to load shed by dropping customers off the grid, starting with factories that have special agreements, in case the combined local production and import is insufficient, and can detatch from neighboring grids and countries if there are import/export issues that could destabilize the grid.

The grid needs to change when supply or load conditions change significantly (e.g., every house in a city suddenly having an EV or heat pump, every house in a city suddenly having solar cells and supplying a ton of power, a power plant or wind farm being built somewhere power has not previously been routed), and can be optimized (e.g., power storage, smart load scheduling), but that is entirely orthogonal to windmills.