Paint effects can be used to good effect if you know what you're doing, especially for just creating the base tree shape.

As to studios, it depends I've seen Speedtree used for background type stuff as to hero elements I have a friend that worked on a tree for I think it was the new jungle book movie and that was all done by hand I believe.

Personally, I like paint effects -> polygons for the base then I use a multi-tile UV on the leaves to get different leaf shapes and shades of colour. From there it's into ZBrush or Mudbox to do the detailing on the trunk and large branches. The benefit of this is you can create a lot of different tree shapes quickly.

Using paint effects well and getting a good result though is not easy. Very easy to produce something that looks awful

Below is an image of a base tree done in pfx then converted to a poly object, this is just the base from here it would need detailing. Took an hour or so to put together and using this as a base I can make many trees very quickly

Dave