Let's take a look at some of the minor league system rankings by different organizations:
MLB Pipeline (MLB official): Not in top 10, exact ranking unknown since MLBP does not provide anything beyond the top 10
ESPN: #12
Bleacher Report: #13
Just so I'm clear, I'm not saying they're the worst farm system, I'm pointing out that their farm system is like their team...a lot of "good" prospects, but little or no "great" prospects. I agree their system ranking in OOTP19 is low, but don't come in here stating their a top 5-10 system and the developers owe you an explanation.
Sources:
https://www.mlb.com/news/top-10-farm...ne/c-267360666
http://bleacherreport.com/articles/2...-start-of-2018
http://www.espn.com/mlb/insider/stor...0-farm-systems (insider required)