Is this really a good complaint?
"Sure we got a young high upside pitcher, but we didn't PAY ENOUGH for one!!"
You spent half the off-season talking about getting cheap, young controllable pitching. The Sox got a 25yo very high upside starter with multiple years left and an expressed desire to sign an extension. You got EXACTLY what you wanted. At some point, can you at least be happy about it?
Carson Kelly is definitely a step up, but he is hardly the only option. And with Teel gone, the Sox can/should now explore catchers with multiple years of control. Since the FA market is just stopgaps and backups, they will probably need to look elsewhere.
One possibility might be Sean Murphy. Atlanta has a good catcher in AAA named Drake Baldwin they could turn to (although I only can speak for his offensive skillset.) With Murphy missing most of last year and being owed $60mill over the next 4 years, I can see them moving on to Baldwin...