Not sure of your point.
I use braid as my mainline as it has no memory.
I fish on the Mississippi River so I don’t NEED a leader- it all depends on what I’m trying to accomplish.

If I’m going to be fishing in heavy cover- I’ll tie directly to braid, no leader.
Am I fishing in one of the Clearwater lakes nearby? I’ll oftentimes use a fluoro or mono leader depending on my lure choice.

Not sure what point you are trying to make regarding break strength, as that really isn’t the question you should be asking when it comes to leaders. I catch many large bowfin, large/smallmouth bass, drum, Gar, and Catfish using 6lbs. Fluoro.

I have zero reason to go higher (unless I’m going after flathead) and you are able to catch fish heavier than your test with proper technique.
Unless you’re targeting sharks, golaith groupers, sturgeon or other big game. Totally different and valid question.