The differences between Shaw and Thompson are striking. Thompson completed only 52% of his pass attempts, but was just as good on 3rd and long as other downs. As a result, he was able to make up for the fewer completions with almost 3 yards more per completion. His interception rate was half Shaw's - 1.6% to 3.1%. The only importantly similarity between the two is that Thompson was also sacked on more than 10% of pass plays.
On the whole, the South Carolina passing game moved the offense. Even after adjusting for schedule, South Carolina was below average on running plays but top 15 on passing plays and top 10 in explosive pass plays (Lattimore was better than Miles, but neither cracked the top 60 in EPA+/run among running backs). On the whole, the offense was borderline top 25.
The defense was borderline top 10 and top 15 against both the run and the pass. The Gamecocks were 2nd in sacks/pass - Clowney's 13 was an important contribution, but South Carolina also had three players with 5 sacks or more and five with 3 sacks or more. They were slightly less impressive getting to the quarterback on passing downs. They prevented explosive pass and run plays, forced a high rate of negative runs, and allowed fewer than 4 points per possession in the red zone.
The lack of a running game and the high sack rates for two different quarterbacks suggest that offensive line play was a problem in 2012. The group in 2013 should look similar to last year's version, but now a year older. South Carolina can only go as far as those five can push back the opposition. While Clowney has been the proud recipient of the ESPN hype machine, the fate of South Carolina's season, in my opinion, rests squarely on Connor Shaw's back (in the medical sense). If Clowney does his best impression of an '09 Ndamukong Suh, the South Carolina defense could slide up into top 5 territory. A decently proficient offense (which must include a viable running game) would put them in the SEC championship game and from there anything can happen.