The only way the trade, and all the events that lead up to it, make sense is if they knew Mookie wouldn't resign here. If that was the case, the front office did the best they could.
As for player development, am I wrong to wish that the Sox would just draft the best hitter available every time and then target pitchers by trade or free agency?
I don't think this is true. From Smiling Joe Hesketh's perspective, you're begging the question by essentially stipulating that they did their best on the basis of facts not in evidence, and then concluding that they did their best on that basis. It's circular.
SJH is saying that they didn't do their best, because he thinks they decided that it was more important to have a sub-Dodgers-level payroll than field the best team possible. That's fair.
Here's my view, in retrospect: if Boston was going to sign Betts, it needed to happen before 2018. And they tried, offering $200m in the offseason between the 2017 and 2018 seasons. At that time, Betts had posted 2 WAR in his partial 2014 season (I'm rounding all of these), 6 (2015), 10 (2016), and 6 (2017). He had earned about $2m. That was the moment. After 2018, when he made $10m and posted 11 more WAR, it was too late. By posting his second 9+ WAR season, he'd cemented himself as an elite player, and he now had enough earnings to self-insure his future — i.e. if he was in a car accident during spring training, he had earned $12m dollars. He was a year closer to FA, so the risk of injury before an FA payday was declining.
They offered him $200m, and he decided to bet on himself. Since then, he's earned almost $50m and now has another $330m pending (I think — it might be more; I'm not sure how this year is being accounted for), so he basically doubled their offer.
We each have to decide for ourselves whether that $200m offer is the equivalent of the $70m starting offer to Lester that was roughly half of what he eventually signed for. I'm not sure it is — Lester was much closer to FA — but I could see how someone with SJH's priors might think that it was. And I'm not sure how big a difference it would have made if they had offered him $240m or $250m or even $300m at that point, because I don't know what Mookie's breakeven point was. I imagine he'd have accepted some deal south of $300m that would sign him into his late thirties (he was 24, so, a 12-15 year deal) and guarantee him a pile of money.
But that's when the decision was made that set us on this path.