If you'll notice the swing. It's not shocking that most people feel like they are the best. But by whose measuring stick? Usually it's by their own.
A person in a competitive k/d team may think they are the best or may say they are best in comparison to some teams and not as good as others. I've seen them with 3.00 k/d or higher. Then put them in a race and we start seeing issues or they'll just quit when the race comes on.
I've also seen K/D players in Captures tend to target the other players instead of looking at the goal of getting the item and they'll protect their k/d and lose the match and then brag about how they owned everyone. It's hilarious, but we tend to focus on our strengths and don't try to build on our weaknesses. I've seen people beat me by a point and then jump on the mic and start yelling how they are the best or see a team play in a way that plays to their strengths and then jeer about how they are the best. They are limited in their playing style because they are protecting the title, "best".
If you build yourself up to say you are the best it's like a house of cards. It has to be meticulously and patiently built up. The problem is one player who is specialized in one thing can bring the whole house down. Then what do you do when the other team is now jeering you as an idiot? I've been able to make winning teams leave because of their bad attitude. They don't want to face a persistent player who is willing to learn their tricks. I just knew how to push their buttons, find the tactics and exploit them. I lose and they rage quit because they knew the damage they took meant they could no longer sustain the smack talk and the loss was coming and then what do they say? They can't stand admitting that they are just regular players.
Play to have fun and use the numbers as a measuring stick of goals. Use them to gauge how you're progressing. If the numbers are still going up you're doing well. If the numbers are going down then ask yourself what you changed badly. And they will fluctuate. One day you'll get caught up in a free roam and you'll realize you spent thousands of dollars on ammo and are down k/d. Lesson learned. Back into a DM and notice those losers won't follow you in because now they're constrained to skill, which they sorely lack.
I love playing people on their turf. They want me to rage quit and I'm using it to learn new techniques so I can stay forever. Why would I be mad, you're doing me a favor! Then when they finally think they've got it all I say, "so when are you going to play me at my game." Crickets.
None of you are the best. You never will be. There will always be a Yin to your Yang and even if you were the best that unstoppable force could be a modder who knows just enough to get away with it. Then I'll hear you say, "whatever" and I'll laugh as I watch your house of cards fall.
What you can be is a confident player, ready for the next challenge, and ready to learn. A great player is one who can get mad during the game, lose and at the end say, "bro, that was great. Thanks for the challenge." A player who can win and isn't afraid to say, "this is what you can do to improve" if asked. In reality, being a great player is easy and takes no skill at all.