Stanley Johnson is 6'-6" and 242 lbs with 7'-0" wingspan. Will Barton is 6'5", 181 lbs, 6'-10" wingspan. I have always thought of Barton as more of a SG/SF tweener (not that there is anything wrong with that). Barton has been a reliable 12-15 pts/gm scorer for several seasons, but he is down this season. Johnson has been a bad shooter for several seasons but was hitting his 3s this season.
I think we could probably get Johnson if we wanted him. I would be OK with that but wouldn't expect him to help all that much. Barton probably has something in mind, not sure where that would be. He will probably help some team some, but probably not all that much.
If we get Barton, we will end up with a very complete unit:
Marcus Smart Derrick White JD Davison (Reg season only)
Jaylen Brown Malcolm Brogdon Payton Pritchard
Jayson Tatum Will Barton Sam Hauser
Al Horford Grant Williams Blake Griffin
Rob Williams Mike Muscala Luke Kornet
That "second" unit is really quite good. And we don't really need Davison for the 3rd unit but he is a nice fit (2-ways cannot play in playoffs unless converted to regular contract, which we cannot do unless we cut someone).