I think the failed bullpen and the failed farm system are actually the same problem, and it wasn't just the bullpen, not having viable 6th and 7th starters wound up costing the Phillies a game or two this year (and they missed the playoffs by a game or two).
Some of it was still very bad luck - both injuries and the crapshoot of pitcher development. But depth is the only hedge against that. Two years ago it looked like we had it - literally a dozen arms that would be contributing as spot starters and useful relievers, even if only 2 or 3 of them truly stuck. Harper talked about how the best way to build a bullpen is from within, but it's not like they haven't tried that, repeatedly. We've got a few candidates now, plus a few guys who might get healthy, but if Klentak (let's just say he stays) runs it back with a bullpen pool of:
Neris, Phelps. Alvarez (re-sign as FA), Morgan, Suarez, Romero, Brogdon, Robertson (minor league deal, could just as easily be Hunter or Parker or someone else), Hembree, Hale
Now, maybe you cut Hembree and Hale loose. Maybe you even move on from Morgan if you think Suarez and Romero are ready. Maybe you don't re-sign Alvarez. But I'm still not sure you hand out another $20-30 million multi-year contract. Maybe one $8-10 million one-year guy.
You need internal depth, but you also need the ability to hit on a Trevor Rosenthal or John Curtiss. It's not like the Phillies didn't have guys like that, they just weren't the right guys this year - or they don't have the right coaches.