That's the conundrum. Ultimately, you normally have to find your best 5 guys to start, even if it means hurting your pen.
Bloom chose to add 2-3 solid pen arms (Jansen, Martin and maybe Joely) and just 1 starter, if you don't count Paxton as 2 and Sale as 3. That pretty much forced Whitlock, Houck, Crawford and maybe eventually Wink to have to start. Had Bloom added 2-3 SP'ers and just Jansen, we'd have seen most of the tweener guys in the pen, assuming good health and production from the rotation.
I think Whitlock wanted a chance to start. That is not reason enough, alone, but he does have the stuff to be a plus starter, so as much as I love him in the pen, I think starting him made sense.
Houck really should have a wider range of pitches to be a starter, and his record the third time through a line-up strongly suggested he not start. Even the difference between his first time through vs the second was great enough to strongly indicate he belongs in the pen, but the fact is, even with that flaw, he's a way better starter than Kluber & Pivetta. He also seems like the better choice over Crawink.
If we can somehow manage to keep Crawink in the pen, all year, and the pen stays healthy, our pen will be the strongest and deepest it's been in a long time.
That helps make the starters better, as we can yank them earlier than in the past and earlier than many other teams can afford to do with their struggling starters in any given game.