I understand the point that a replacement starter would not get the same number of innings as a good starter, and agree with the need to combine a number of reliever innings with starter innings for the comparison. But why use replacement-level relief innings to fill the gap, rather than league-average relief innings.

A team is deciding between Starter A and Replacement Starter B, not Starter A and the combination of Replacement Starter B + Replacement Reliever C. If the team goes with Replacement Starter B, the missing innings will be filled in by the major league bullpen, not Replacement Reliever C, and over the course of the season, all the innings used to support replacement level starters across the league will by definition be league-average innings.

Is this right, or am I missing something?

I can see where there may be some trouble, since we can perhaps assume that long relievers will be relied upon more to fill in those extra innings, and they tend to be lower quality relievers than the late inning guys. But a point in the other direction could be made arguing that a team saving money on a replacement-level starter may spend a bit more for the bullpen. In any event, I’d think league-average is closer to the truth than replacement level for those extra relief innings.

He’s a two pitch pitcher, which seriously limits his potential as a starter. His pitches obviously lack the sort of break that makes them effective at middling velocity (as revealed by this inability to miss bats out of the zone.)

Reasonably assume that he gets 2-3 MPH back on his fastball out of the bullpen, and optimistically assume he’s advanced his control but this is being over shadowed by his inability to miss bats, and further optimistically assume that his control can stick around with that extra 2-3 miles an hour. That’s a lot of assumptions, and two of them aren’t especailly likely, but if they all come together he’s could be an 8th inning pitcher.

Because at this point, I can’t imagine a team seeing potential in him as a starter.