As I understand it, outside ISO needs a 5 out-lineup to clear out for the player to be successful, and inside ISO needs a 4 out, 1-inside lineup.
Looking at the box scores in hindsight, it looks like Uruguay has some poor OD on their bigs, so a patient with a guard at C/PF and switched for D may have been a good option against them. I haven't followed U21 too much, but I imagine since there's more focus on primaries, that may be the case for many teams.