Levels 5 plus are entirely skill based, and you should never die here, ever. There still exists an element of luck to the amount of points you can harvest on these levels, but no amount of bad randomness should ever lead to death.
EDIT: Actually, saying never is not accurate. Every once in a blue moon you'll encounter a pie factory that is literally not passable because fireballs will block both ladders until the timer expires. It's an extremely rare occurrence and no such obstacle exists on any of the other boards. The next closest thing is having to deal with a derpy freezer on the 6th girder of a barrel board, but that situation is passable and it's likely your fault when it happens anyway.
I agree that too many people blame luck for their deaths (way) too much of the time, and the "I got 'x' far at 'y' pace talk drives me crazy too.
However, I think your annoyance with this is blinding you a little and pushing you to an extreme position to the contrary that isn't reasonable.
"True screwings" are absolutely real. The fireballs (and even the barrels now and then) are capable of creating genuinely intractable situations that can't be traced back to player error or sub-optimal decision making.
I've just seen too much stuff like this:http://www.twitch.tv/chrisp_kreme/c/2880632
to ever say that there are no screwings outside of the specific ones you mentioned.
And even for the ones you mentioned, I don't think it's fair to say that a fireball getting to the 6th girder is "likely your fault". All it takes is for a fireball to slip through and get one girder above you and he pretty much has his ticket punched for the 6th girder, if he decides that's where he wants to go. There are many, many ways for this slip-through to happen without the player doing anything wrong.
I'd say that the belief that "there are no screwings" is an illusion that stems from the fireballs rarely creating as many of the worst-case scenarios that they COULD create. But I think a couple hours on a hypothetical "maximum fireball nastiness" ROMset would dispel the illusion pretty quick. If the fireballs really want to hose you, they can, and they will, whether on barrels, conveyors, or rivets.
However, I'm in full agreement with you that the bigger illusion, and the far more pernicious one, is seeing "impossibly" bad luck where it doesn't exist, and I do think people need to take more responsibility.
But a polarized view, either way ("there is too much luck" or "there is no luck"), is unhealthy.