If you don't use early returns don't you end up with functions doing lots of state/variable mutation (within the function)? Thats what I consider the problem with big function and/or not using early returns. You then need to keep track of all those modification. I find it much easier to reason with early returns.

You can certainly over-engineer things just to avoid bigger functions. However from my experience I see that far less than complicated large functions with little care to readability.