I did some statcasting at the link. But the tl;dr is that the very limited statcast data we have on him from this spring is pretty sterling.
He's got just three tracked balls, but all three are over 100 MPH including an opposite field triple at 106. You wouldn't necessarily think it, but going 106 the opposite way in the air is extremely impressive. 148 guys in MLB managed it a single time last year. 74 did it more than once, only 15 did it at least five times. Hernandez did it in one of his first three tracked balls, so chances are decent that's not even where he currently tops out.
Based on the handful of guys I looked at, their actual max exit velo was 5-6 MPH higher than their opposite field in the air max. So that'd give Cristian an implied max in the ~112 range. That would put him in line with guys like Marcus Semien, Randy Arozarena, and Wyatt Langford. As a 21 year old shortstop.
He only had 5 homeruns last year, so I don't want to get too over my skis. But it looks like he has at least 55 or 60 grade raw power *today*. He's of course got to turn that raw into production before any of this matters but it looks like the special skillset we were promised when he signed is there.