I'm not sure I agree that we rushed Betts. The kid was killing every level he moved up to from day one. Plus, we called him up in 2014 when we were already out of it, so what was the need "rush"? His .812 OPS in MLB those 2 months in 2014 is not evidence of being rushed.
On Leon, I wouldn't be so quick to say his offense has "obviously gotten better" based on just a tiny sample size of 35 PAs. I'm not saying he can't be improving. Of course, he can be. It's natural for players to slowly improve over time, especially at, before and around the age that Leon currently is (27).
Leon has been in professional baseball since age 18. That's 10 years! I'm sorry, but I'm not buying the idea that suddenly, 10 years into his career, he suddenly found the magic potion. Sure, I'm fine with slower growth, and there are cases where players have seemingly vastly improved almost overnight without apparent PED use, but more times than not, what we are seeing from Leon recently, turns out to be no more than a "flash in the pan". The odds are Leon will return to numbers much closer to his career norms (.580 MLB OPS in 270 PAs/.654 minor league OPS).
One reason I am not a believer just yet, is that Leon had a .655 OPS at AAA this year in 115 PAs. This was nearly identical to his minor league career OPS, so one could argue he showed no signs of improvement prior to his call-up. However, I would argue he has shown improvement in recent years, but just not on the scale of these 35 PAs. Leon was first called up to AAA briefly in 2012 after a very lack-luster .614 OPS at the AA level in 510 PAs. Here are his AAA numbers since 2012:
2012 1.026 in 64 PAs
(2013: he was returned to A- and AA ball with a .542 OPS at AA)
2014: .692 in 193 PAs/ .447 in MLB (70 PAs with the NATs)
2015: .676 in 111 PAs/.439 in 128 PAs with BOS
2016: .655 in 130 PAs at Pawtucket
He's consistently been over his AA OPS every year at AAA, so I do see strong signs of improvement, but nothing massive. I think Leon projects at about .650-.675 in the bigs, and that may be generous.
Can he do much better? Yes, of course he can, but I wouldn't bet on it.