This is silly and just wrong. You're erroneous on multiple levels:
1) Sacks are just a part of what the d-line does. I would argue it's not even the most important function that they perform. Hell, it may not even be the second most important function. They need to maintain their gaps in the running game and pressure the qb. If they create a pressure, even if it doesn't result in a sack, the QB will be less likely to make a good decision. Sacks are rare, and should not be used as the sole indicator of d-line play.
2) You ignore that the Bears added significant depth not only at defensive end, but also at defensive tackle. Last year, our depth was Nate Collins. After that, we were screwed. While I get that your point is starting defensive lineman, you say "People who think we upgraded don't know stats or football." However, people who think we've upgraded also take into account that our depth far exceeds that of last year because those same people understand football enough to know that you need a good rotation of d-lineman. A point you seem to completely miss.
3) The stat itself is revisionist history. You're looking at the starting defensive line from 2012 (a year where our defense was insane). The 2013 defensive line was much much worse than the 2012 defensive line. Julius Peppers got old. Henry Melton was injured. Stephen Paea played injured. And Shea McClellin sucked. An accurate measure of whether or not our d-line has improved from last year, if you're basing it solely on sacks, would be to view it from 2013, since, you know, the defensive line actually played in 2013. Otherwise, you're twisting numbers to meet your hypothesis. Here you go:
Julius Peppers 7.0 sacks
Henry Melton 0.0
Stephen Paea 1.5
Shea McClellin 4.0
Jared Allen 11.5
Jeremiah Ratliff 1.5
Stephen Paea 1.5
Lamarr Houston 6.0
In other words, the accurate statistic would be the old Bears d-line from 2013 produced 12.5 sacks. The new Bears defensive line produced 20.5 sacks. That would be an upgrade, even in your completely skewed category.
In sum, you're arguing a fallacy. The defensive line is vastly improved.