First, I'm not selling him as anything other than interesting. The Braves are the ones apparently scouting him.
Second, I think Castellanos is a good hitter who can improve the Braves depth and bench. Whether or not he starts at any particular position, I don't know. Clearly his defense is not good. But it needs to be noted he's better vs LHP and RHP than Camargo with the bat. His defense seems to suck. I haven't spent any great time watching him play but the numbers sure seem to show that.
Third, I don't particularly believe in Camargo. He played clearly above his head in Mar/April. Since then he's been a 108 wRC+ whose walk rate is regressing to his norm. That said, I'm not sure it will make sense to upgrade Camargo this trade season. It should definitely be on the agenda this offseason. Depending on where some of the 3B pieces fall, Atlanta may well be in a position to do just that.