That is nowhere near as robust as MLB’s farm system. I think they would develop better players if they set one up. Heck, that is why they bring in so many foreign players, they come through programs that emphasize skill development over time.
The problem is to get a farm system as robust as the MLB or NHL you need fan buy in. Minor league baseball and hockey work to develop players because they work as leagues with enough fan support that they can function on their own (as shown during various work stoppages in the major leagues). The failure of NFL Europe, the XFL, the “suspended” Arena season, and the fact almost nobody even remembers the NBA even HAS a d-league show that there isn’t that kind of fan support for minor leagues in those sports.
I wonder how much the success of the college sports feeds into the inability to have minor leagues for these. College hockey and baseball aren’t very popular, and are often considered dumping grounds for bad players that will never make it in the pros even the minor leagues. They’re addendums to the sport. Meanwhile college football and basketball are HUGE, rivaling in popularity their pro leagues. I don’t think there’s enough oxygen in their rooms for minor league football or basketball unless they’re HEAVILY funded by their majors.