If by MLS development you mean the league I am less invested in that as I am about development of players in MLS. I think player development, at least for some clubs, has come on leaps and bounds over the last decade. The closing of the residency program in Bradenton was critical to this development as it exploded the pool of players who could be considered. For decades the US player pool was determined by who got the invite to Bradenton, and that was determined by who knew who. With the launch of the academies the geographic reach of clubs, and therefore the national team, increased exponentially. Take just my old hometown of Birmingham. The money that FC Dallas poured into their academy meant that they could bring in two players, Chris Richards (FC Bayern now) and Tanner Tessman (at FC Dallas) who would likely never be found previously. In just the last few years Dallas has produced Weston McKennie (Juve), Reggie Cannon (Bovista), Richards, Bryan Reynolds (Roma), along with Paxton Pomykal and Tessman who will be next to move. NYRB and Salt Lake have also done great with their academies. Reyna came out of NYCFC. Basically, with the exception of Pulisic I think all of the non-Euro national team members came out of MLS academies.