Heck, this year I've always thought of the bullpen as a strength even though there have definitely been some bad moments/games. It's always great, however, to see some stats from moonslav to back that impression up.
Another--no doubt specious--way of looking at the bullpen is to say that the five best (Walden, Workman, Brasier, Barnes, Hembree) are paid a total of $5.1M and their combined WAR is 4.2. The top four starters (Price, Sale, Porcello, ERod) are paid a total of $88M and their combined WAR is 4.8. "Wait just a minute," you are no doubt thinking. "What about the cotton-picking innings pitched?" Glad you asked. The starters (just those 4) have pitched a humoungous 330 innings, and the weakling bullpen (just those 5) have pitched a paltry 166 innings, which is almost exactly half of what the starters have thrown.
In other words, DD has spent a fortune on the rotation, and nickels and dimes on the bullpen, and the latter are pretty much outperforming the former.
So I wouldn't recommend that DD go after another expensive starter, but probably get some bullpen help. Reinforce success, not failure.