Think of the benefits of KAT being on the Celtics, he and Tatum can share full-length fur coats. 
This won't happen without Brown being involved.
This type of sentiment is just not reality. The vast majority of superstar trades from the last decade did not involve an all-star going back.
Take Harden for example. The Nets traded Jarrett Allen (roughly equivalent to Rob Williams) and Caris Lavert, a player who had three straight signficant injury-ridden seasons and was injured again for a fourth season, who at his best is a ball-dominant guard with meh efficiency. They also traded 3 firsts and offered 4 swaps.
This is the format. Look at the George, Anthony, Cousins, Davis, etc. trades. This is generally the format.
The real question is whether or not a team like the Hawks could beat our offer, which I think they probably could, depending on how the Wolves valued Williams vs Collins.