I was actually looking at the
USA Basketball leadership page a few days ago because of this very issue. From what I can tell, Grant Hill is the managing director of the men's 5x5 national team. He does not handle the women's side, men's 3x3, or any junior teams.
Jay Demings directs the 3x3 national teams, men and women. He chairs the 3-person committees that select both teams. He deserves some credit for past successes and some blame for current failures. I imagine he'll do a lot of soul-searching as we move forward.
Your idea of the NBA senior tour taking over 3x3 is an interesting option. This version of the sport, such as it is, could experience a lot of growth before Los Angeles 2028. Ice Cube's
Big3 has been around since 2017, and there's a 3x3 women's league,
Unrivaled, starting up soon. The latter is offering enough money to sway active WNBA players.
We (as a country) have yet to decide how dedicated we should be to what is essentially a different event, with different courts and rules and such. Maybe we should consider 3x3 as a full-time gig, and not just something that 5x5 players do when they're moonlighting. It's so new that you could see another country that's not historically good at 5x5 divert their resources into establishing themselves as a 3x3 power, and they'd probably make a dent rather quickly.