TL;DR is probably E) all of the above... I think all of ours guys are hard workers and good kids / young adults, but I think we have some deficiencies that have led to us seeing younger guys play a good bit.
Proctor - talented... But I'm in the group that thinks he should weigh < = to 350. Struggles with speed which destroys his footwork.
Dewberry - doesn't get the push you need from a guy his size and too slow for the pulling DeBoer uses in this offense.
Brailsford - heart and soul of the line with a super genius IQ for making the line calls, but smaller and simply isn't going to move that guy who is 30-50 lbs bigger. As Scotty notes... You canna change the laws of physics.
Vandermark - Plus 1 guy that can play any position. We need one of him every year... But I wonder where is overall talent level is. Seems like a hard worker who does whatever he is asked, and does it pretty well.
Roberts - Injured... ? Pass blocking.
Formby - Hard working dude, a step slow for an SEC tackle, but has quietly graded out very well last few weeks. Again, struggles with speed and that is a double whammy on both sides of the line.
We've played some solid freshmen. Carrol and the freshmen guard look solid. We have a number of guys in Ionata, Roq, and Alinen who are working hard in the background and have a good combo of size and power for the interior.
I think the other issue is that our running backs just have not evinced any vision even when there are holes, creases, and gaps for them... It isn't all on the OL. Again, I think we have a hard working group, there just isn't a Najee Harris amongst them.
I can't really weigh in on the coaching... past my skill level. The downside to playing so many combos is that the OL is really the one position where you need a starting 5 and you don't sub until the game is in hand. Another year in this offense with the current guys (plus a solid portal or two) should pay some dividends. Need to get better speed installed at the tackles, and a bigger center will offset the losses of Brailsford's leadership and IQ.
And... Kudos to SC's DL. Those guys played well and are very talented and took us to the woodshed. Have to give them lots of credit!