At what elo are you no longer a bad player?

Yes. We are in agreement.

They're not always skewed upwards though. There are titled players on here whose ratings are clearly below their FIDE rating, which can indeed be verified through open sources on the Internet. Maybe they use their daily / blitz games on here for training purposes. Maybe they play them blindfolded. I have no idea. But I there is an IM I played on here who is around 1970 in daily, but he's FIDE 2477, just to give an example, and it's far from the only case of this I've seen. 

Depends on who you ask but objectively,everyone who is average or above average tournament player is not a bad player. In terms of rating ,the lower end would equate to around 1500-1700 depending on the country you play in.

I know for myself I use blitz for messing around, and use rapid for serious practice.

I'm guessing that's what high rated people do.

Many high rated people don't play rapid... Because of all the Cheating. 

The standard that says "I know the basics of opening and endgame principles, tactics, and strategy," has generally been 1200.  I've coached high school players and I'd say 1100 OTB means a solid player who has enough skill to occasionally beat much better players.

Some of us high-rated players consider ourselves to be dreadfully bad chess players.

Me too, but I'm not high rated.  

It is a rare player under 1500 who will create the correct plan for White in this ending, and not many below 1800 will execute it correctly even after finding the correct plan.

I was 1700 on the best online playing site in 2006 when I created the right plan and then blew the ending in this game.

ISn't it possible to walk with the king to the queenside and start grabbing pawns there. Black has no moves at his disposal other than Rf6 and then back to Rf7. He connot move the bishop or the king. He cannot move the rook from the f file. Even if black gives a few spite checks when the king tries to cross the e-file black will have to eventually return his rook to the f file and then he will be in semi zugzwang again just as in the starting position.

the only way he can get out of this is by sacrificing a pawn with g5 but then that extra pawn can matter for white.

I peaked as a uscf a player, and consider my chess abilities nothing special.

Non sequitur.

Yes, that's the basic idea, which I understood at the time. But White also can improve matters on the kingside first.

Not a chance that the gap between 2200 and 2500 is greater than the gap between 0 and 2200. A player rated E1800-E2000 stands a decent chance of gaining a draw against a GM of E2500 (I defeated an IM when I was rated around E1800.) Magnus Carlsen was nearly E2700 when he dropped a draw against an amateur rated about E2050.

The last King Salman Rapid championship round 1 Carlsen (2903) loses to Tukhaev (2556)!

Agreed. I've drawn with a 2477 IM. I have absolutely no doubt that  I was taking the game a lot more seriously than him, and that 9 times out of 10, he would beat me comfortably. And, I guess in at least six of the games, the defeat would be pretty crushing. But if someone of that level gives a competent amateur chances, they can easily be punished. On the other hand a decent amateur can play a beginner without their queen, and still win quite comfortably.