You can make what you want of this, but last year Kevin Correia and Scott Diamond had remarkably similar results.
In terms of innings pitched, Diamond ranked 80th and Correia 81st among major league pitchers.
Diamond faced 714 batters and got 173 innings pitched. Correia faced 728 batters and got 171 innings pitched.
Diamond gave up 184 hits, Correia 176.
Diamond struck out 90 and Correia 89.
The only large differences are that Correia walks a lot more batters, 46 compared to 31 for Diamond. And, probably at least partially as a result, Diamond gave up fewer earned runs, 68 compared to Correia's 80.
To be blunt, none of those differences are really very meaningful The obvious advantage Diamond has is that he is young and therefore likely to improve. The advantage Correia has is that he has a longer track record and last year was not far from his career norms. But, based solely on their performance last year, these two can be expected to produce at about the same level.
As I said at the beginning, you can make what you want of that. I think it ought to temper any certainty you have about Diamond or doubts you might have about Correia.