Tromp was 5'11 175 when signed in 2011, like a lot of LA players I suspect he's filled out since then.
He's from Aruba, which isn't exactly a hotbed of LA talent, so he was probably very raw when signed.
Winkelman had him at 47 this spring, but I'd bet after his good year at Reading, he'll break into the top 30 lists, he had him projected as the Clearwater LF this season, but Tromp obviously impressed the FO this spring and was promoted:
"At the plate Tromp’s swing is a bit stiff, but he has quieted it from his earlier days, leaving a short and powerful path to the ball. This year he cut down on his strikeouts, making an even larger improvement after his midseason promotion to Clearwater. The only problem is that his aggressiveness caused his walk rate to drop after the promotion. Tromp has above average speed, but has not translated that into good stolen base success. In the field Tromp continues to move down the defensive spectrum and now looks to be a left fielder long term."
I'd point out if you looked at Altherr in 2014, a mediocre season at Reading at age 23, wasn't even ranked going into 2015.
(he was ranked #9 in 2014, but put that in perspective, M Gonzalez #4, Tocci #6, Martin #7, and S Gonzalez #10 - pitiful farm system that year)
Then had a breakout year at Reading/Lehigh in 2015. Became a more selective hitter. Took another jump this year when Stairs adjusted his swing.
Tromp is another kid who struggled with plate discipline but seems to have turned the corner.