Sloppy writing is the one that leads to asspulls, i think you understand that.I only agree that it was sloppy writing, but I don't consider it an asspull.
It's really not that big of a shock to me that Bijuu's can absorb natural energy. I always suspected as much anyhow ever seen they shown Kurama meditate his chakra back.
Seems to me you tend to over think stuff and proceed with your own unsupported explanations.
Except your meditate chakra back holds no value since that chakra didnt turn out to be senjutsu in manga, so it was flawed hypothesis but lucky guess.