Today we continue our summer reviews of the pre-season Top 20 Prospects lists with the Seattle Mariners.
This is a review of the pre-season list.
It is not a new list.
These are the pre-season grades.
This list was originally published January 7, 2026
1) Alex Jackson, OF, Grade B+: 2014 first-rounder, slow start in Low-A (.157/.240/.213 in 108 at-bats), better after going down to short-season A (.259/.355/.444), currently out with hand injury after missing time with shoulder problem. He was advertised as the best high school bat in the ’14 class with power and an advanced approach. That is not what we saw in the Midwest League; he was overaggressive and had serious contact issues. Just 19 of course but the split between what he was supposed to be and what he currently is, is quite wide.
2) D.J. Peterson, 1B-3B, Grade B+: 2013 first-rounder hitting .223/.287/.344 with seven homers, 31 walks, 93 strikeouts in 372 at-bats between Double-A and Triple-A. Struggling to tap his power against advanced pitching.
3) Edwin Diaz, RHP, Grade B/B-: Excellent in High-A (1.70, 42/9 K/BB in 37 innings) and decent enough in Double-A (3.96, 77/27 K/BB in 75 innings), age 21, mechanics, slider, and change-up all sharper this year to go with solid fastball. Good progression.
4) Austin Wilson, OF, Grade B/B-: Hitting .228/.332/.346 with seven homers, 27 walks, 85 strikeouts in 289 at-bats in High-A. This is not very good, especially for a college product in the California League.
5) Gabby Guerrero, OF, Grade B-/B: Traded to Arizona Diamondbacks, hitting .225/.264/.359 with six homers, 20 walks, 87 strikeouts in 365 at-bats. Tools not translating against advanced pitching.
6) Ketel Marte, SS, Grade B-/B: Hey here’s a guy hitting as expected, .321/.366/.417 between Double-A and Triple-A, recently promoted to majors. Only 21 years old, bright future.
7) Patrick Kivlehan, OF-3B-1B, Grade B-: Hitting .239/.303/.430 with 17 homers, 13 steals, 30 walks, 88 strikeouts in 351 at-bats in Triple-A. Still has interesting power/speed combo, has cut back on strikeouts. Not sure how he fits on roster.
8) Tyler O’Neill, OF, Grade B-/C+: Power! .253/.300/.541 with 25 homers. Surprising speed! 16 steals in 16 attempts. Bad plate discipline too! 19 walks, 104 strikeouts.
9) Victor Sanchez, RHP, Grade B-/C+: Passed on following swimming accident.
10) Luiz Gohara, LHP, Grade C+: 4.12 ERA with 44/21 K/BB in 44 innings, 48 hits between Low-A and short-season ball. Just 19, pitching better than last year due to better command, though still has a way to go.
11) Ryan Yarbrough, LHP, Grade C+: 3.99 ERA with 54/15 K/BB in 70 innings, 82 hits combined between Low-A and High-A. Hittable, but throws strikes, as expected.
12) Carson Smith, RHP, Grade C+: Successful in major league pen, 2.82 ERA with 58/13 K/BB in 45 innings, just 31 hits, 11 saves in 13 attempts.
13) Danny Hultzen, LHP, Grade C+: Pitched eight innings, back on the DL with shoulder problems. Not expected to pitch the rest of the year.
14) Tyler Marlette, C, Grade C+: Hitting .227/.290/.377 between High-A and Double-A, 20 walks, 51 strikeouts in 247 at-bats. Another disappointing bat.
15) Brayan Hernandez, OF, Grade C+: Hitting .238/.313/.350 with two homers, 16 strikeouts, 35 walks in 143 at-bats in Dominican Summer League. Too far away for the numbers to be meaningful. Signed for $2,000,000 in 2014, expected to hit for average but not doing so yet.
16) Jordy Lara, 1B, Grade C+: Hitting .235/.316/.366 with 34 walks, 60 strikeouts in 336 at-bats in Double-A. He hit well at the same level last year (.286/.326/.492) so this is another discouragement.
17) Tyler Olson, LHP, Grade C+/C: Split season between Triple-A (5.14, 30/11 in 28, 40 hits) and the majors (5.40, 8/10 in 13, 18 hits). Likely to bounce back and forth for some time.
18) John Hicks, C, Grade C: Hitting .247/.290/.371 with five homers, 17 walks, 56 strikeouts in 251 at-bats in Triple-A. Solid defender.
19) Mayckol Guaipe, RHP, Grade C: 3.02 ERA with 31/10 K/BB in 42 innings, 46 hits in Triple-A. In the majors now, 9.95 in 6.1 innings, 11 hits, seven runs, but a 6/1 K/BB. Can be useful bullpen part.
20) Jabari Henry, OF, Grade C: .166/.267/.295 in 217 at-bats in Double-A. Yuck.
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The other Jabari is better, Jabari Blash hitting .266/.364/.529 with 21 homers, 46 walks, 99 strikeouts in 331 at-bats in the high minors.
The Mariners system has had a bad year in most respects and this list has not turned out too well on the offensive side: hitters like Jackson and Peterson are supposed to be quite advanced but haven’t lived up to the billing, in some cases to a very disturbing extent. New names to watch include outfielder Luis Liberato (drawing good reviews in the Northwest League), toolsy Gareth Morgan (great tools but also 62 strikeouts in 150 at-bats in rookie ball, little progress from last year), and Ramon Flores, acquired from the Yankees.
On the pitching side, lefty Mike Montgomery didn’t live up to his potential in the Royals and Rays systems but has found himself with Seattle, posting a 3.07 ERA with a 56/27 K/BB in 76 innings. He is a good reminder why teams don’t want to give up on live-armed lefties. Carson Smith has been strong in the bullpen. On the other hand, Danny Hultzen is a big questionmark once again, though generally speaking the pitching is in better shape than the hitting.
I don’t have any answers here but am very interested in observations and opinions from readers who follow the Mariners system closely. What would you do with this organization? Is there something truly wrong with hitting development or is it bad luck?
