Jason Marquis has spent his entire career on life support. He's finished a season with his ERA over six twice and under four twice; he's was 33-years-old before he pushed his K:BB ratio over two for the first time in his career. He's a sinkerballer who allowed 1.3 home runs per nine innings while pitching for Dave Duncan. Baseball Reference says he's worth six wins above replacement as a pitcher (in 1852 innings) and four as a hitter (in 679 plate appearances.)
For a while I was surprised—every time I saw him in a new uniform—that Jason Marquis was still playing baseball. Eventually the surprise turned on itself, ate its own tail, and on my deathbed, now, I think I'll be surprised when someone tells me he isn't stashed somewhere in the back of the Raleigh-Durham BattleKatzz's bullpen.
For all that, he's now 118-111 in a career that looked like it could have been over before he turned 30.
Shelby Miller will probably never catch Marquis as a hitter, but at the rate he's going he might have already matched the best pitching season of Marquis's career, per rWAR. That distinction is one of the reasons replacement level made intuitive sense to me in the first place—it explains how the shape of Marquis's value is different from, say, Kyle Lohse's or Shelby Miller's.
You don't want to end up with Jason Marquis in your rotation all year. He's replaceable, and the players you can replace him with are usually more pleasant to watch on the mound, if not at the plate. But he'll soak up innings, and every so often he'll turn in an above-soaked performance. There's value there—he's a major-league baseball player—it's just not value you want to draw on.
The St. Louis Cardinals have dug up nearly all of their front-line prospects—which is why it's a little weird that whether the Cardinals should bring up the last one, Michael Wacha, has become such a flashpoint. Now we're into the prospects for which Cy Young Awards are not the 90th-percentile projection.
Tyler Lyons and John Gast—and Joe Kelly—can all hope for better individual seasons than Jason Marquis ever had, at least if you're starting from his peripherals. But Jason Marquis is going to cross 2000 innings pitched in his career, and now he's beaten the Cardinals six times. All of them could certainly do worse.