Exactly . Chris sale was traded and he was cost controlled for 3 years and how much did the Sox get for him ? A look back: https://www.baseballtradevalues.com/this-trade-in-history-chris-sale-to-the-red-sox/
Moncada is, at this time, considered the #1 prospect in baseball by Fangraphs (who rate him a 70, which is rare); #2 overall in the sport by both Baseball America and MLB Pipeline; and #5 by Baseball Prospectus.
In other words, there is strong consensus that he’ll be a future star, and his stats validate it: at age 21, he put up a 156 WRC+ at High-A, followed by a 152 WRC+ at AA, which earned him a late-season cup of coffee with the big club. There’s some doubt about whether he’ll land at 2B or 3B, but no one doubts that his bat will be elite. You rarely see a prospect with a triple-digit valuation, but this one seems justified.
*Kopech is, at this time, ranked #32 at Baseball America, #10 at MLB Pipeline, and #36 at Baseball Prospectus. Fangraphs rates him a 55 (on the traditional scouting scale of 20-80, where 50 is considered good). All of that suggests he’ll be a future impact arm – most likely as a #2 starter – although Eric Longenhagen of Fangraphs does note that comes with risk – he’s had some injury issues and off-field incidents, and his high-octane velo coupled with delivery issues suggests some reliever risk.
Basabe was projected as maybe a 4th OF type and Victor Diaz was a throw in RHP.
Soto has 2.5 years left and his salary is not cost controlled. He'll be getting record arbitration numbers. The Sox don't have a Moncada type and Montgomery might be too far away for the Nats to consider him a Top Ten Prospect but realistically that's where Montgomery is headed but he has to continue doing the things he's doing now for another season for him to reach the top 10.
Colas isn't ranked in the Top 100 . He might get there at the end of the year if he continues to crush at AA. He had some good exposure getting to the Futures game and the players in that game are just the types the Nats want ,AA and AAA type high ranking players. Colas is older than Soto but a better athlete, better fielder easily, LH like Soto . He might have to crack the Top 50 prospects list but that isn't going to happen before the Nats trade him unless it doesn't happen by the deadline. Considering it's Cola's 1st year, he's adjusted well and hopefully he climbs through the system faster now. He's now at a level where he's age appropriate so raking at Birmingham would mean Colas might also be a fast riser and crack the Top 100 whenever they do them again in the winter. But as an older player in his 1st year , he just hasn't been around long enough and hadn't been seen throughout an American HS and College career to get highly ranked .He may already be a Top 50 guy by some scouts estimations but it won't show in rankings.
The cost controlled salary Sale had means a lot more to potential suitors than Soto's whatever he gets in arbitration numbers means to his suitors . He has less years remaining than Sale did. But he is an everyday player whose hitting is so good it makes up for his fielding. He may never get to 7 fWAR again but for the next 2.5 he should be around 15 fWAR if he stays healthy which is always a concern .
Sox got 1 great hitting and speed prospect and 1 very good pitching prospect a guy with a 50/50 chance of having a MLB career and a throw in pitcher who had 93 innings , nothing above A ball and nothing outstanding in his over all numbers but had a live arm. The Red Sox prospects in their system were ranked 1, 3, 8 and 28.
https://www.mlbtraderumors.com/2016/12/red-sox-to-acquire-chris-sale.html