I think plants grown outdoors when compared to plants grown indoors will get bigger.
My theory (I don't even know if you can call it a theory) is that the sun is far away so it's stretching towards the source of the light.
Of course I could be extremely wrong, don't take anything I said as fact.
The plants aren't stretching indoors because they don't have a nighttime, and often have more intense luminosity than the sun. Plants grown outdoors don't stretch out nearly as much in flower, instead they do most of it during in veg which opens up room for branches.
If you were to reduce your lights time you can accomplish the same indoors as well. But this is a bad thing. Artificial light is affected by the inverse square law and loses luminosity at a distance. Unlike the sun which is roughly 10,000 lumens at all times in any place it hits regardless of elevation (distance). That's why plants grown outdoors tend to finish at the same time while plants grown indoors usually always have premature lower limbs.