A lot of people were taken by surprise when the Diamondbacks non-tendered Welington Castillo, but it did at least set up an inevitability. It felt like a foregone conclusion that Castillo would end up signing with the Orioles. It was only a matter of the contract length. Castillo was said to want three years. The Orioles were said to want not that.

The arrangement now, as has been reported: Castillo has signed with Baltimore for one year and $6 million. He also has a second-year player option, worth $7 million. So Castillo won’t go broke, and now the Orioles have another power bat they can install in the lineup. In that sense, hey, mission accomplished for everyone. The only issue for the Orioles is that Castillo still doesn’t seem like he should be the starter.

The issue with Castillo isn’t his age. He won’t turn 30 until the end of next April. It isn’t his bat, because it’s pretty solid, as catchers go. And it isn’t his durability — Castillo has played in more than 100 games four years in a row. It all looks fine, except for the one thing. You already know what that one thing is, because this is no longer fresh and novel information, but it’s still worth bringing up.

Why didn’t the new Diamondbacks front office love Castillo? His defense. Why couldn’t Castillo sign in the market for more than he did? His defense. Behind the plate, Castillo is defensively-challenged, and much of that comes down to his receiving. Using the numbers at Baseball Prospectus, Castillo has never scored well, and the league gets that more than it ever has.

To draw the direct comparison, yes, my position is that Welington Castillo is worse than Caleb Joseph. That’s the same Caleb Joseph who just finished with a wRC+ of literally 6. He didn’t record a single RBI! I don’t think that version of Joseph is of any use. But I don’t believe that’s the real Joseph, so, here are some numbers.

Over the past three years, Castillo has notched a 94 wRC+. Joseph, a meager 67. On a per-450-PA basis, Castillo gets the offensive edge by 13.3 runs.

As the Steamer projections go, Castillo is projected for an 88 wRC+. Joseph comes in at 69. On a per-450-PA basis, Castillo gets the offensive edge by 9.3 runs.

There is zero question that Castillo swings the more powerful bat. Anyone can see that, and that’s any player’s most conspicuous skill. The bat is why Castillo even has a big-league job. Over a full catcher year, Castillo is about 10 runs better than Joseph. Maybe even 15, if you believe Joseph is in some sort of decline.

Call it 15 runs. Whatever. It doesn’t matter. Using the Baseball Prospectus data, I’ve also calculated fielding performance over the past three years, per 450 plate appearances. We get Castillo at -11.6 runs. And Joseph? He’s at +20.0. Joseph doesn’t hit much; he’s maybe 15 runs worse than Castillo is. But Castillo doesn’t field much; he’s maybe 30 runs worse than Joseph is. We’re not arguing over narrow differences here. We’re not even arguing! The case is made. Joseph’s defensive advantage is something like twice as significant as Castillo’s edge at the plate. Joseph has been a phenomenal catcher, and it stands to reason a staff like Baltimore’s could use that.

I know it can be hard to talk yourself into believing this. It feels like it would take a lot of extra strikes to make up for some kind of disadvantage in hitting home runs. But the differences at the plate come down to a relatively small number of opportunities. There are thousands upon thousands of opportunities to receive a pitch the batter takes. A large fraction of those pitches are in the vicinity of some edge, and I don’t really need to tell you how little things, little advantages or disadvantages can add up. That’s how we get extreme framing numbers in the first place. This is an old conversation.

Regress the numbers if you like. You’re regressing a difference of something like 15 or 20 runs of value. It’s tough to regress away Joseph’s lead, so any good argument against him has to rest on the belief that his 2016 performance at the plate was incredibly meaningful. I don’t know why 141 plate appearances would be more meaningful than the 630 that preceded them. And I’ll just note right here that, in the middle of last season, Joseph required surgery on his testicles.

The market hasn’t been giving full credit to good receivers, and worse receivers haven’t had to pay the full penalty. The Diamondbacks replaced Castillo with Jeff Mathis, but he got just $4 million over two years. Still, you can see the effects. The Diamondbacks couldn’t find a trade partner for Castillo, with his having an expected salary around $5.9 million. His deal with Baltimore has a similar value. Castillo is the same age as Jason Castro, and Castillo is the slightly better hitter, but Castro got three guaranteed years, for $24.5 million. Castro has been a tremendous defensive catcher, so the Twins were thrilled to bring him in. His defensive ability isn’t getting him as much money as equivalent offensive ability would, but the defense helps determine where teams look for help in the first place. It’s caught on, and it’s not going away.

Castillo isn’t a bad player. He remains capable of more good than harm. It’s just, looking at things overall, my belief is that Caleb Joseph would be the superior starting option. The Orioles’ path back to contention is already narrow. They can’t really afford to too often leave value on the bench.