I think some of the problems in offensive playcalling is this desire to protect the rookie QB. I think that's both to protect him from hits (Daniels takes too many hits despite his escapability) and from making mistakes (Daniels makes so may fewer mistakes than a typical rookie that I'd like them to take the leash off him.) I also think that some of the offensive conservatism is because Kingsbury doesn't completely trust this line and may think he is limited by his weapons.
You are probably right that Kingsbury (and I am betting Daniels himself) doesn't completely trust this line, but just in watching different sequences in different games, it just looks like Kingsbury is a bit more predictable. There will be big sequences where I feel like I can predict Danies dropping back, and in those sequences there are a lot of sacks. In other games, when I try to do the same things, they break runs fairly often - and I am talking about the NFC elite in the Eagles and Lions. It just seems like in the modern NFL, play-calling mix of run/pass is really key to keeping defenses off-balance, and committing to that scheme is a key component of success for a lot of the league's elite.
I agree with you though, it is really hard to separate things like this from, for example, the talent on OL. Sometimes that "unpredictability" is greatly affected by the OL's ability to have some measure of control at the line. In other words, if the DL gets decent penetration, then look at how the outcomes start to shake out:
1) Running play? With good penetration, many runs are going to end up snuffed.
2) Passing play? With an athletic QB, this play may still succeed. However, if penetration is by just the front-4 or 3, you are probably in trouble here unless there is a scramble that can break.
There are a lot of variables at play but the less your OL can win battles consistently - you are definitely right, your hands start getting tied and sometimes that can look like a lack of creativity.
^^ After all that, to my eyes, I still do see signs of a lack of creativity. I still see some signs of bad coaching at critical times. I didn't like the critical plays against the Eagles, where Kliff called consecutive up-the-gut running plays right into Jalen Carter who had been breaking through. Also, coaching/scheme could have helped Terry against the Eagles more than it did; I think there was a big lack of dynamism in how they were getting Terry opportunities. So, there are some troubling signs and that was a big L. That was a winnable game in my eyes. Hopefully we see signs of growth by the coaches in these last few games. The Titans game showed some good signs, but the Saints game looked like a regression in some ways (not judging by score here; just again, talking about offensive creativity, moving guys around, multi-TE sets, other aspects that I have felt were lacking in other games).