I think Pearson may have a bit more potential and long term upside than Manoah, but Pearson has also has a well-documented injury history and he just can't seem to stay healthy. Comparatively, Manoah is a horse who doesn't overthrow his capability, stays healthy and so far in the minors he gets the job done. There have been plenty of top prospects who flamed out at the major league level fo a variety of reasons. At the end of the day, it really doesn't matter a lick how much potential both pitchers have, or how fast they light up the radar gun. The only things that really matter at the major league level are:
1) How consistent is any given player from game to game, from month to month and from season to season?;
2) How well does a give player stay healthy and take care of his body and mind?;
3) Does the player have personal demons like lack of confidence, bad temper, booze/drug addictions or abuse issues
(think Roberto Osuna, who as of May 15th, 2021 still doesn't have a contract for 2021) which will sooner or late cause him
to flame out?;
4) Whether or not any given player can get the job done between he lines.
5.) Is the player a good teammate, or a selfish, egotistical jerk like Barry Bonds? Teams will overlook a selfish player as long as he keeps producing. But once that player cools off at the plate or can't get his pitches over for strikes, he'll be gone as soon as it can be arranged.
There have been plenty of "practise tigers" ove rthe years who look really good between starts or in practise when there's no presure on them. But or whatever reason(s), he just can't make the leap from AAA to MLB. Generally speaking, if a player hasn't made it to the big leaguies by age 27, he's probably going to be a career minor leaguer. There's no shame in that; only the best of the best get to be superstars in any occupation.