There are a few points here.
1. There is a reason a team like Boston would trade Moncada and not Devers, who the Sox reportedly wanted but the Red Sox wouldn't include him and instead went with Moncada. Smart teams know who the true keepers are, and who have more red flags. The same can be said for Kopech and Giolitio
2. People often overlook the job of a GM, and all that goes into it outside of player acquisition. Say Rick Hahn was in charge of a marketing department. He hires 2 brand new creatives, 2 hires that come from big agencies and have a good track record. When they arrive to work, they are set up with two desktop computers from 1998. Not really setting up your new investments for success, are you? The training staff and baseball analytics department is woefully behind the times, and we've seen it impact the Sox on the field over the last handful of years. The "core" of this team basically never plays together at the same time.
3. Sports is unfair. Being a GM is unfair. I don't disagree that on paper, Rick Hahn built a solid core during the rebuild. The names listed in your post, on paper, make up a solid foundation. For whatever reason, it didn't work. The biggest issue is we said from Day 1 of the rebuild, as excited as were for each name listed above, some of them weren't going to work out. They never do, for any baseball team. Prospects fail. You know it's going to happen, and you need to be prepared for it when it does happen. The next wave of talent needs to be there. That's maybe the biggest failure of the Sox. They went all in on their core, and had NOTHING to back it up. The minor league system is a barren wasteland with almost no MLB talent. That means they have to spend in FA, which 95% of the time is a fools errand.