If Alcantara does indeed turn out to be the key guy, his stock has fallen. Before this past season, Eric Longenhagen ranked him third in the Cardinals’ system, and now he ranks fifth. Alcantara’s strikeouts went backwards, and he’s still showing inconsistent control of his big-time fastball. Because Alcantara has yet to make more of his peak velocity, there are real concerns he ends up in the bullpen. All of his major-league appearances with the Cardinals were made as a reliever. The Marlins, presumably, will let him keep starting. He instantly becomes a jewel in their own system, as the organization hopes he learns where his fastball is going.
Alcantara isn’t an easy talent for the Cardinals to lose. All teams love their good prospects. Yet Alcantara wasn’t likely to be a major factor in 2018, and Ozuna’s coming off a season in which he was worth 4.8 WAR. The Cardinals might tell you they’re enamored of Ozuna’s intimidation factor. I don’t know to what extent that makes a difference; the Cardinals could already hit. But Ozuna will provide something that was missing, a dynamism for a team with otherwise lower-ceiling regulars.
I saw Alcantara last year, iirc. He had no idea where the ball was going and walked seemingly every batter he faced. His whippy arm, long/loose frame, height, and obvious velocity make him a scout's wet dream, but he still has to get it all together before he's worth a lick of salt. Best of luck to him, he has the attributes and i hope he figures it all out.
edit: and looking at a recent instagram post showing off his new hair color(s), it looks like carlos has a tattoo of a necklace while he happens to be wearing a real necklace.