Three promising MLB prospects—pitcher Harrison, speedster Simpson and outfielder Merrill—have all shown flashes of brilliance but remain far from the breakout performances fans expected. Their 2024‑2025 seasons illustrate how development timelines can stretch well beyond a single rookie year .

Harrison's 31.9% strikeout rate ranks third among 50‑plus‑inning pitchers

After accelerating through the minors and debuting in 2023, Harrison posted a 7‑7 record with a 4.56 ERA over 24 starts in his 2024 rookie campaign. according to the source, his 31.9% strikeout rate this season places him third among pitchers who have logged at least 50 innings.

Milwaukee Brewers, who acquired him following a spring‑training option to the minors, have seen his fastball climb from 92.6 mph to 95 mph and his slurve deliver an 11‑inch horizontal break.. Statcast now rates his fastball in the 95th percentile and his breaking ball in the 96th,a combination that mirrors the Brewers’ successful reclamation of Quinn Priester a year earlier.

Shoulder inflammation limited his velocity last year, but a raise in his arm slot from 24 to 33 degrees has yielded a more consistent delivery, according to the report. While his three consecutive scoreless outings in late May and a 12‑strikeout start in early June suggest upward momentum, he remains a work‑in‑progress.

Simpson's .433 ACC batting average and 44 steals raise questions on power‑less value

Former UAB transfer Simpson led the ACC in 2022 with a .433 average and only 16 strikeouts in 241 plate appearances, though he hit just one home run. The Rays selected him in the second round, and he posted a .295/.326/.345 line with 44 steals as a rookie in 2025.

His contact rate consistently ranks among the top three in the league, fueling an offense built on speed rather than power. In April 2025 he hit .314 with a .349 on‑base percentage, projecting a 0.9 WAR through May and a potential 3 WAR for the full season. However, a May slump to .245/.278 and a dip in defensive performance in center field have sparked debate about the long‑term value of a profile lacking power and walks.

As the source reported, Simpson’s left‑field metrics are “excellent,” but his overall contribution hinges on whether he can sustain the April surge without the cushion of extra‑base hits.

Merrill's 4.8 WAR rookie season fades as 2025 slump deepens

High‑school phenom Merrill was a late first‑round pick in 2021, shifted from shortstop to center field, and earned a spot on the 2024 Opening Day roster at age 21... He generated 4.8 WAR as a rookie,handling the defensive transition with poise.

Since that breakout, his numbers have regressed sharply, and a slow start to the 2025 campaign has left analysts uncertain about the cause. the source notes that “the reasons for this decline are uncertain,” but emphasizes that Merrill still possesses the talent to rebound.

His case underscores a broader pattern: early success does not guarantee a linear trajectory, especially when players are asked to adapt to new postiions at the major‑league level.

Who will finally break out among the dozen prospects?

While the report examines a dozen young players, it leaves three key questions unanswered: Which prospect will sustain improvement beyond a single hot stretch? How will teams like Milwaukee and Tampa Bay tailor coaching to address each player’s specific deficiencies? And what role will injuries, such as Harrison’s shoulder inflammation, play in shaping future performance?

These gaps highlight the difficulty of projecting long‑term value from limited sample sizes, a challenge that scouts and fans alike continue to grapple with.