For people having trouble with this game against real players, go play the bots on the default difficulty. Get the feeling for not panicking in a shootout and unloading your whole clip when in reality all you need to do is just fire when you're actually going to hit the person. Trust me, this made all the difference in the world for me. You would be stunned how many players empty their entire clip already, and are looking for some desperate melee attempt, meanwhile because I was more accurate and conservative with my clip, a lot of fights end with me having extra bullets to spare and the other guy is a sitting duck.
You unload or empty your entire clip because you get scared of the fact that the other guy is firing in your general direction and may be hitting you, but remember that this is a game where you have a shield up until they can break it down. What I realized was the key to Halo Infinite MP was stop reacting too crazily and swinging the right analog stick wildly just because you engage with someone. Slowly (as difficult as this may be able to process mid gun fight) put your crosshair where it needs to be and you might be shocked at the outcome. Sometimes that's not possible because they already have you in trouble, and if it continues as is you won't win. But most shootouts tend to be ones you have a legit opportunity to win.
Doing things this way, not wasting bullets and being more careful to slowly align my crosshair on my targets, I end up getting more 2, 3 or even 4 back to back kills. This game is going to be fucking heaven in campaign.