I think Prieto is going to have issues in MLB. He doesn't walk a ton and since he doesn't have even double-digit home run power, he'll probably walk even less in MLB. He's not remotely a shortstop which limits his value as a utility infielder, and his glove isn't an asset anywhere in the infield. I think if everything breaks right, he could be a second-division starter at second base for a handful of years, or maybe a bench piece on a contender. Basically, he's Hanser Alberto.
That's a decent career depending on how you define decent. But you're 100% right that he was never going to sniff the majors in Baltimore.