this is true, in a cover 2 defense DE's don't get so many tackles, where schobel had been rackign up quite a few tackles, (71,73, and 60 the previous 3 years) in the previous system. In the tampa 2 system, the DE is going to get more stats from sacking quarterbacks. For example, Simeon Rice, a premier DE in that system never got more than 50 tackles in a season, but would get a ton of sacks (Of course it helps to have a great D like tampa typically has working behind them). This year with tampa being in a state of flux, Rice only has 9 tackles and 1 sack, and do you think anyone in tampa is thinking that he is overrated?
Also, people have to take into account that he gets more attention than Denney or Kelsay, so he gets less tackles due to more double teaming. If you took Schobel off this D-line, kelsay and denney would not be having the stats that they do at the time, and offenses would be carving this defense up even more.