They are still separate though because international is still a free market in terms of who you can attempt to sign. There's a monetary restriction, to say nothing of the politics and under the table stuff, but the players are all free agents. Domestic draft, they aren't. The two sets of players are also scouted by an entirely different group of people.
Trade gets like Marsh and Sanchez and Sosa also reflect successful development, that you turned into a different asset.
I doubt the Phillies' success rate is especially unusual, especially if we're only talking about the Top 15 teams in terms of either payroll or making the playoffs (if they aren't ever in the playoffs who cares if they develop 100% of their players. And while money is also a crutch, those teams can't ever sign a Harper or a Wheeler to begin with). Everybody probably has four or five guys on their roster who were low draft picks or cheap int'l signings.
We have long seen the Dodgers as being much better than the Phillies for much longer in every area, correctly, but they are largely a trade and free agent-built team now too. Braves obviously are missing extremely key guys but beat us with only 1 out of 9 homegrown position players last night.
But it's not exactly news that the Phillies didn't develop much of anyone from 2015-2017, and they also shipped out most of their limited good young players for a few years after that (Crawford, Alfaro, Sixto, Howard - only one of whom panned out). The effects of that still linger especially combined with worse international.
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