Here's my thing, it's easy to look back and question the Simmons move, but it's so easy to forget how bad Simmons was looking with the bat. Consider these stats:
2012: .289 avg, .751 OPS, 3 HR's, 12 BB's
2013: .248 avg, .692 OPS, 17 HR's, 40 BB's
2014: .244 avg, .617 OPS, 7 HR's, 32 BB's
2015: .265 avg, .659 OPS, 4 HR's, 39 BB's
2016: .281 avg, .690 OPS, 4 HR's, 28 BB's (first year with Angels)
Of course we all know how 2017 turned out. But legitimately, it looked like his development was headed in the wrong direction, and at best we'd have an all glove player, with a chance he didn't even hit enough to be a major leaguer.
So this is not a defense to saying we did the right thing, but he was legitimately one of the worst hitters in the league for a couple of years there. 2017 was pretty unexpected.
Compared to what they have now at SS? At least Simmons was known to be an elite defender. Even with the bad hitting Simmons was still a 2-3 win player.
Simmons' best seasons offensively came when he pulled the most fly balls. He is a glowing example of why guys want to pull more fly balls. If the Braves had an analytics department larger than 1 guy and an intern they would have had him make the same changes he made 2017.
As I said, I can't fault the Braves too much for trading a guy who provided most of his value on defense before his defense declined. What I fault them for is wasting other valuable assets by keeping them. Trading Simmons and holding onto Teheran was an inexcusable set of moves for a team to make.