I'm not putting them all in one category...yes, you're right, they do overlap.

Some pros use arrangers...some amateurs use workstations...but these situations are generally not the norm, and are usually the exception....in fact, in all probability, there are probably more amateurs using workstations than pros using arrangers.

Arrangers are simply made for home use first...some pros are smart enough to find them useful for solo gigging.

And, maybe the word "pro" doesn't quite nail it...perhaps the words "advanced player" might be better.

Ian