Difference between ONI and UNSC training?

I just finished reading New Blood a couple days ago (yea it took me a while to get around to reading it) and something interesting came up. Buck insinuates that Veronica could easily take him down due to her “ONI training”. ONI training was specifically mentioned in another piece of Halo material as well, which happened to be Nightfall. It’s also implied there that ONI training is supposed to be quite a big deal. Vale is also exceptionally good in CQC and she happens to be with ONI as well.

My question is why does it seem like those who go through ONI training are so much better or at least implied to be in terms of hand to hand combat and CQC than the ones who just receive basic?

Your right especially since buck received ODST training which is special forces. Interesting indeed.

I think we can draw parallels with our world.

Agents who work for an intelligence agency are bound to receive better training than their regular military forces.

For instance, KBG agents, especially with regards to hand combat, receive more rigorous training than the Russian Army Forces. The same could be told about the CIA and US Army.

Also, the higher training is possible because intelligence agencies recruit selectively. The armed forces can take in anyone with a pulse and a fully functional body.