I don't think the offense can be said to run through the left guard, but I do think it speaks to how badly Jared Goff relies on having a healthy offensive line. If there is a single missing piece, he folds, which causes the entire offense to fold... When you're considering giving him an extension, you might as well sign the entire offensive line with him or you're screwed.
As for the defense, Glenn has to shoulder some of the blame (for the third straight season), but Holmes does too. It bears repeating that the defensive weaknesses that are prevalent are not some new problem. This board was clamoring three weeks ago at the deadline for a pass rusher across from Hutchinson and for secondary help and Holmes didn't address either. 8-3 isn't time to even approach the panic button, but 8-5 isn't inconceivable at this point with road games against New Orleans and Chicago upcoming. At that point, I would be worried.