Chris Heisey wOBA by year
That's not the profile of a player who "doesn't hit." Actually, over the past few years that he's gotten about 300 AB, Heisey has been above league-standard twice (2010, 2011) and basically league-average once (2012).
Let's look at Ludwick.
Outside of his 2012 "resurrection", Ludwick was arguably a less productive hitter than Heisey over the past three years. Bolstered by a crazy lineup in StL in 2008, he posted his career best of wOBA of .408, but other than that, his numbers are pretty pedestrian. Add in below average defense and the fact that he's six years older than Heisey, and you get the argument that Keri is making.
Come to think of it, I think Keri's point is actually a relatively benign one given the numbers he could have cited. If he wanted to, he could actually have argued that Heisey should have been the starter all along. But he didn't. He made a qualified claim that it "wasn't too much of a stretch" to consider Heisey a competent replacement for Ludwick.
As I've mentioned, this is hardly a "ridiculous" or "absurd" comment on Keri's part. It's actually just a measured observation by a careful writer who has an opinion to share.
And let's not forget that Ludwick's 2012 hitting was largely driven by luck (which even FanGraphs grants is the residue of design and of taking low-cost gambles when they are available on the FA market, but which is less of an opportunity when it means plunking down $7.5 million a year).