Some utterly simplistic thoughts about the bullpen and the absence of Kelly and likely absence of Kimbrel.
1. I looked at last year's regular season Red Sox stats, specifically the top 14 in WAR's: Sale, 6.9, Price 4.4, Porcello 3.1, ERod 3.0, Kimbrel 2.3, Wright 1.7, Velazquez 1.4, Brasier 1.5, Barnes 1.1, Workman .9, Eovaldi .8, Poyner .6, Hembree .5, and Kelly .5. I would preliminarily argue that the last year's bullpen did just fine with mostly those 14 and that Kelly--despite his great pitching in the postseason--won't be missed much.
2. Note also that the the rotation leads the parade in WAR value (unless your name is Pomeranz, whose WAR was -.5) for the pitching staff because they carry the load on innings. Thus the Sox (DD) investment in starters, especially Price, Porcello, and Sale.
3. As for Kimbrel, I have never been a big fan of his because he basically doesn't do windows, which means he rarely pitches in the 8th or comes in with men on base. On top of that, he expects a long-term contract. So me, I'm happy with taking the risk of losing him even though other teams are willing to spend heavily to have great bullpens--none, however, have yet met the demands of Kimbrel and his agent Dave Meter.
4. If Wright's knee holds up, he will make a huge difference in the bullpen which he demonstrated last year.
5. I agree I'm ignoring the current thinking about starters--try to keep them from facing a lineup more than three times in a game or even twice. Last year I wrote I was impressed with how the Rays manager did that by starting a reliever to get thru at least the top part of the order before bringing in his starter.