Damn. I was hoping I could get some useful tips. You seem to be operating under the assumption that an NT manager makes all the decisions by himself, and has zero accountability or transparency. I know this isn't the case at all for the US, and I'm fairly sure it's not the case for most of the top teams in the world.
A: There's almost never two players that are so equal that this happens. Even if skills are equal, some players are training, some managers are better at game shape management, etc. Your top reason assumes that some players are equally good for the final selection spots, they both will receive equal training, and their managers are equally reliable for game management. And then you assume that the NT manager happens to have 1 of these guys. Or you assume that he chooses his own player despite the guy being a worse choice, and no one holds him accountable.
Most importantly, if the NT manager ends up winning gold, it's a pretty difficult argument that he took a suboptimal selection to benefit himself.
B: Correct! I know the skills of the major US players in the NBBA. Except, uh, so does everyone else. If the NT manager went around adding all the players of his opponents just to check their skills, don't you think they'd be annoyed? Don't you think they would vote for someone else the next election? If a player is close to selection, everyone knows his skills anyway. I don't have any more info than anyone else in the NBBA can get.
C: I'm doing a terrible job. I somehow haven't been able to force managers to tell me when they're selling players. Winning worlds gold was good, but I could do better by reading the minds of other managers to I know when players are going to be listed. I also don't see how I get an advantage here, how does this help me win a D1 title? You're assuming here that a D1 competitor wants to purchase a certain type of player, but they, for some reason, aren't prepared for it. They'll never be prepared to purchase anyone if that's the case.
Look - if you abuse the privilege of being NT manager, you can certainly get a small benefit. But you won't get elected again. This isn't a systemic problem, and definitely not a problem with managers like rwystyrk, or any others that you're considering knocking accomplishments from because they were NT managers. I know it's not easier to win D1 titles as NT manager because if it was, NT elections would be flooded with D1 candidates. And they're not.