What happened over time is that they learned to build them better. They scaled up gradually over time. Now, the latest turbines going in the ground are right back to 1.5 megawatts, but now they work. So they have gradually learned, and made really small adjustments over time. So they are just that much more efficient.
Wind farms can still have negative impacts on the environment.
The one big thing against wind power has been concern about birds. It's always something. But what it looks like is that what was killing birds is the little fast machines. With the new big slow-moving turbines, the probability of a bird strike goes way down. And these days they do a lot of prescreening.