Circling back around to the Chourio projection, I was curious how other 20 year olds who got regular playing time ended up performing in their age 21 seasons.
Using the leaderboards at FanGraphs it looks there have been 32 players in the Expansion Era to have gotten at least 400 PAs in their age 20 season with Chourio coming in at 117 wRC+ (10th) and 3.9 WAR (9th), not too shabby.
For the comparisons below I lopped off 1970 Jack Heidemann who was clearly overmatched for his whole career and 1980 Lloyd Moseby (had a nice run with 118 wRC+ and 22.0 WAR from age 23-27 though) at the bottom of the list, then Mike Trout/AlexRodriguez at the top of the list since they were clearly in a whole other league of their own, plus 2019 Juan Soto & Vlad Junior since their age 21 seasons were in the shortened 2020, which leaves the following 25 players...
1989 Gary Sheffield
20: 405 PAs | 82 wRC+ | -0.4 WAR
21: 547 PAs | 118 wRC+ | 2.9 WAR
2008 Justin Upton
20: 417 PAs | 106 wRC+ | 0.6 WAR
21: 588 PAs | 130 wRC+ | 4.9 WAR
2014 Rougned Odor
20: 417 PAs | 91 wRC+ | 1.0 WAR
21: 470 PAs | 107 wRC+ | 2.5 WAR
1997 Edgar Renteria
20: 691 PAs | 81 wRC+ | 1.0 WAR
21: 580 PAs | 90 wRC+ | 0.9 WAR
1976 Robin Yount
20: 690 PAs | 72 wRC+ | 1.1 WAR
21: 663 PAs | 95 wRC+ | 2.4 WAR
1978 Clint Hurdle
20: 481 PAs | 111 wRC+ | 1.2 WAR
21: 204 PAs | 94 wRC+ | 0.0 WAR
1971 Cesar Cedeno
20: 649 PAs | 94 wRC+ | 1.3 WAR
21: 625 PAs | 163 wRC+ | 7.8 WAR
1972 Buddy Bell
20: 505 PAs | 93 wRC+ | 1.5 WAR
21: 689 PAs | 100 wRC+ | 3.6 WAR
1986 Ruben Sierra
20: 411 PAs | 103 wRC+ | 1.6 WAR
21: 696 PAs | 95 wRC+ | 0.9 WAR
2010 Starlin Castro
20: 506 PAs | 99 wRC+ | 1.8 WAR
21: 715 PAs | 109 wRC+ | 2.7 WAR
1975 Rick Manning
20: 535 PAs | 102 wRC+ | 2.1 WAR
21: 606 PAs | 116 wRC+ | 2.7 WAR
1992 Ivan Rodriguez
20: 454 PAs | 85 wRC+ | 2.3 WAR
21: 519 PAs | 94 wRC+ | 2.4 WAR
1978 Alan Trammell
20: 504 PAs | 90 wRC+ | 2.7 WAR
21: 520 PAs | 87 wRC+ | 0.4 WAR
2009 Elvis Andrus
20: 541 PAs | 81 wRC+ | 3.3 WAR
21: 674 PAs | 75 wRC+ | 2.1 WAR
1999 Adrian Beltre
20: 614 PAs | 100 wRC+ | 3.4 WAR
21: 575 PAs | 116 wRC+ | 3.9 WAR
2015 Carlos Correa
20: 432 PAs | 136 wRC+ | 3.4 WAR
21: 660 PAs | 123 wRC+ | 4.1 WAR
1976 Butch Wynegar
20: 622 PAs | 113 wRC+ | 3.6 WAR
21: 617 PAs | 95 wRC+ | 3.0 WAR
1997 Andruw Jones
20: 467 PAs | 96 wRC+ | 3.7 WAR
21: 631 PAs | 113 wRC+ | 7.0 WAR
1975 Claudell Washington
20: 635 PAs | 120 wRC+ | 3.8 WAR
21: 530 PAs | 94 wRC+ | 0.1 WAR
1988 Roberto Alomar
20: 611 PAs | 107 wRC+ | 3.9 WAR
21: 702 PAs | 110 wRC+ | 3.8 WAR
2013 Bryce Harper
20: 497 PAs | 137 wRC+ | 4.1 WAR
21: 395 PAs | 115 wRC+ | 1.6 WAR
2018 Ronald Acuna Jr.
20: 487 PAs | 142 wRC+ | 4.4 WAR
21: 715 PAs | 125 wRC+ | 4.8 WAR
2010 Jason Heyward
20: 623 PAs | 134 wRC+ | 4.7 WAR
21: 456 PAs | 96 wRC+ | 1.9 WAR
2013 Manny Machado
20: 710 PAs | 102 wRC+ | 5.0 WAR
21: 354 PAs | 111 wRC+ | 2.3 WAR
1990 Ken Griffey Jr.
20: 666 PAs | 132 wRC+ | 5.0 WAR
21: 633 PAs | 148 wRC+ | 6.9 WAR
So all told I'd say something like 17 of those 25 players (or 19 of 27 if you include Soto and Vlad Jr) have had at least HofVG careers, which is a pretty nice ratio, and I'd break down their progressions from age 20 to age 21 as such...
QUANTUM LEAPERS (4 for +17.4 WAR)
1971 Cesar Cedeno (+6.5 WAR), 2008 Justin Upton (+4.3 WAR), 1997 Andruw Jones (+3.3 WAR), 1989 Gary Sheffield (+3.3 WAR)
NICE GAINERS (4 for +6.8 WAR)
1972 Buddy Bell (+2.1 WAR), 1990 Ken Griffey Jr. (+1.9 WAR), 2014 Rougned Odor (+1.5 WAR), 1976 Robin Yount (+1.3 WAR)
BOUT THE SAMERS (10 for +1.7 WAR)
2010 Starlin Castro (+0.9 WAR), 2015 Carlos Correa (+0.7 WAR), 1975 Rick Manning (+0.6 WAR), 1999 Adrian Beltre (+0.5 WAR), 2018 Ronald Acuna Jr. (+0.4 WAR), 1992 Ivan Rodriguez (+0.1 WAR), 1988 Roberto Alomar (-0.1 WAR), 1997 Edgar Renteria (-0.1 WAR),1976 Butch Wynegar (-0.6 WAR), 1986 Ruben Sierra (-0.7 WAR)
LIL STUMBLERS (2 for -2.4 WAR)
1978 Clint Hurdle (-1.2 WAR), 2009 Elvis Andrus (-1.2 WAR)
BIG DROPPERS (5 for -13.0 WAR)
1975 Claudell Washington (-3.7 WAR), 2013 Bryce Harper (-2.5 WAR), 2013 Manny Machado (-2.7 WAR), 2010 Jason Heyward (-2.8 WAR), 1978 Alan Trammell (-2.3 WAR)