Yeah lack of transparency is just never ending story but it is true in every life situation. As they say - information age.
If those pros / streamers would not just pop-up out of nowhere doing crazy stuff, post their early videos, post their progress it would be more transparent and believable.
The problem is that people don't record them being "average" or worse, they don't bother posting that as none will watch (until they make it) and so on.
Thus in combination what EA / Respawn does and what information is publicly available for masses = yeah it just makes you think 100% cheaters above Diamond 1 or even below that.
In reality there are those prodigies, your Donks, your Raphas, your Simples and so on. I am 100% sure those guys must be legit. So it is possible to be THAT much better than average player it is just that in Apex (and many more games) you don't see their progress, don't understand how they do what they do, yourself don't work on your skill and game analysis = creates total black hole of hopeless playing.
And let's add to that reality - 0.00001% (or close to that) ever make it to pro in anything basically. So you being worse than pros is actually a 99.9999999% normal thing, and you being worse than top10% probably is as well. The issue with Apex is that this "top10%" these days is more like top20% and you start to wonder how come there are soooo many good players yet they don't get to pro, in many cases disappear.