I think that's kind of a false limit, tbh. I don't think a player has to become an all-star to be productive and valuable to a team. And there have been plenty of players who were drafted, did a stint in the G League (or D League, as was) and came back to be various levels of productive.
These include Danny Green, who played 20 games for the Cavs his rookie season before getting waived and picked up by the Spurs, who sent him to the D League for several months. Hassan Whiteside, also, who played dozens and dozens of games in the G League. Robert Covington was a UDFA who got picked up by Houston and then spent basically the entire rookie year in the D League.
Other names include Derrick Jones, Spencer Dinwiddie, Ish Smith, Seth Curry, Dwayne Dedmon, Gerald Green, Justin Holiday, and Anthony Tolliver.