SO and FR just isnt accurate. Your two deep overall is as follows:

Offense-
SR- 4
JR-5
SO-8
RFr- 1
TFr- 4

Defense-
Sr- 2
Jr-4
So-8
RFr-4
TFr-3

ST- 2 sophomore kickers and a freshman long snapper.

So overall- you have 6 seniors, 9 juniors, 18 sophomores, 5 redshirt freshman, 7 8 true freshman in your depth chart including special teams. that is 30/45 for a 66.67% of your depth chart. On defense- 15/21 on your two deep are Fr/So which equates to 71.4%.

Take UVA for example on their depth chart-

SR- 13
JR- 10
SO-22
RFr- 4
TFr-7

Just on defense, heres the two deep breakdown:
Sr- 4
Jr-3
So-11
RFr-1
Tf-3

33-56 players are freshman and sophomores for a percentage of 59%. On defense, 15/22 are freshman or sophomores. Is 7% more freshman and sophomores that drastic of a difference? On defense, the two teams are playing the same amount of freshman and sophomores. I don't think the problem is personnel. At this point, it may be scheme.