Genuine top 6 centers are so damn hard to land. They're probably the most precious commodity in hockey, which is why GMs are incredibly reluctant to let the good ones get away. If you look at all the recent Cup winners, in the vast majority of cases their top centers were originally drafted by those teams. The Blues are the anomaly in the fact that they brought in both O'Reilly and Schenn from elsewhere, but then they are easily the weakest (at least on paper) Cup winning team in years.
So whatever money the Bruins have to play with, getting someone good is still going to be very difficult. All the guys in this list are good players, but Hertl and Strome are the only two I see as possibly becoming available, and if they do they'll be in demand and Strome is arguably the weakest guy on the list. Sweeney's going to need to work some magic, of a kind well beyond what he's demonstrated to date, or he's going to have to hope that Studnicka takes a massive leap forward in the next 6-12 months. Otherwise the Bruins could be looking pretty bleak down the middle for quite awhile. Selecting only Stud, JFK and a player they already knew had a bottom 6 ceiling in Frederic as high pick centers in the drafts prior to 2019 was so so stupid and costly.