It's probably many of these things plus a few not on the list. I'm not sure we can even pinpoint one area that is mostly worthy of the blame game.
Our pen was weak to start with. The hope was they could hold it together until we traded for someone(s). They did well for a while, but ultimately came down to earth and even underground.
Timely hitting is not something that can be coached, managed, traded for or inspired. It is not a sustainable skill set. It may involve luck, momentum or whatever, but it's hard to throw blame on anyone for doing poorly in small subset sample sizes, but the fact is, we have lost many games due to the lack of one key hit.
Our SP'ers have pitched poorly and not gone long into games. Our 5th starter has been a punching bag. Without some massive run support, at times, our 5th starters would be something like 2-15.
Devers, Vaz and Bogey have stepped it up, even in the clutch, but too many have declined.
I've not given up hope, yet, but I am as low as I have been since 2017.