And how many blank checkbooks has he been handed?
Don't forget when he took over, the Sox had some $300 million tied up in Price, Sale and Eovladi, and the oft-injured Eovaldi was looking like the healthiest of the three. Not to mention the whole Betts situation, where he was reportedly adamant aboiut not signing any extension that didn't break some sort of record. And after all that, there were still 21 (now 22) other roster spots to fill. And all this for a team that won 84 games and missed the post-season. (And was only 6 games better than Cherington's last place 2015 team.)
Was he supposed to keep pumping money into it and hope it all somehow came together?
Not to mention, the whole narrative of "he has only managed small market teams and doesn't know how to manage big ones" is patently false. Not one small market GM in MLB history has gone to a large market team and kept his small market budget (without being told to do so). When Dan Duquette came over from Montreal, did he keep spending like he still ran the Expos? (If anything, one could argue that what Duquette did not know how to do was spend responsibly.)