Detection is made more difficult by the fact that some players are actually really good. I've been playing Fortnite for only a couple weeks now on the Switch, and I can easily kill ~60% of players. I'm sure that with more practice I could get within the top three pretty consistently.
The cheating issue in any successful game really is a case of only being able to tame the blatant cheats down to the point of every player you encounter being "plausibly just that good" while monitoring for the cheating software so that a ban sweep can be done later. Pretty much every time Fortnite does a major patch now, a wave of bans goes through and the player population suddenly becomes much weaker.
Likewise I've gone through periods where I'll play Counter-Strike casuals and it's even more dramatic in some respects. Players will show up in the server and the atmosphere changes suddenly - I'll make the same kinds of plays as before, performing apparently similarly, and yet my K/D will bottom out, without even directly interacting with that player at all. It's like they sucked the air out of the room, and they'll get on the voice chat and spew garbage about how high or drunk they are right now. Then they leave and my K/D pops right back up again.
So I've concluded that online gaming always tends towards being an illusion world - a rough approximation of ability at best, but mostly a venue for untrammeled predatory behavior.
I still put up with it because it really engages my masochistic tendencies to try to "beat the cheater", and most games have techniques that let you do this to some degree.
From the few hours I played it seems to me that the problem is just the lack of skill based matchmaking. If you don't sink countless hours in the game you will get your ass kicked in a few seconds by the ones who do for obvious reasons.
That makes the game not very enjoyable for casual players IMO but unfortunately the most vocal player base is the one that play the most (obviously) and they made it clear to Epic Games when they mentioned thinking about skill based MM that they want to keep their easy kills.
I’m a casual player too, and when I started playing, word of mouth was just spreading and I was somewhere in the middle, now when I play it I’m 1 shot killed every time.
I think as time has gone on the amount of people who practise every day and have got good has risen. I don’t think it’s anything underhand, it’s the same with a lot of games, once the popularity rises it becomes impossible to play.
(I play on PS4)
Many games I've played in the past when at their peak of popularity had plenty of bad players. The popularity was a continuous draw of new players which had little experience. However, as the games popularity waned, then only the true die-hards remained.
Maybe Fortnite is already past the peak curve in on-ramping new comers.
Higher TTK ensures that players with good movement and map control can have the stack and weapons required to out-live and out-damage better aimers in a fight.
However, as a casual player, I'm amazed at how good everyone seems to be. Everyone seems better than me. Especially at aiming. I'm one shot killed all the time. I also casually play Quake Champions and Unreal Tournament. However, in those games, I generally am somewhere in the middle. Most games I find at least some people not as good as I am.