I don't think Atlanta would do Smart for Collins straight up, but I'd certainly do that.
Smart, Williams (either one), and maybe a 21 1st
I think that makes more sense value wise as Collins is clearly the best player in that trade. I like Smart, but Collins is just better. Snell is due to play any day now so he provides some quality depth at SG.
Post Trade - Healthy roster
Starters - Walker, Brown, Tatum, Collins, Thompson
Rotation - Teague, Snell, Pritchard, Langford, Theis, Williams (the other one)
Deep Bench - Nesmith, Ojeleye, Edwards, Green
TW - Waters, Fall
I think that team is much more balanced for this year, but I'd do the trade more for the future. I think Collins could be the 3rd guy on a contender when when Tatum and Brown are at peak potential in the future, so I'd do the trade for that reason alone. Obviously have to keep Collins, but I'd be all in for that as the team needs his size and skill set a lot more than they need Smart.