The easy way to design Battlegrounds: A straightforward system in which minions are offered completely at random, without regard to the player's rating or middle name or astrological sign.
The hard way to design Battlegrounds: Some convoluted algorithm that -- for some reason? -- attempts to keep certain players from breaking through to higher rankings by denying them triples and making sure their unprotected power minions get sniped.
Which one do you suppose Blizzard went for?
One explanation for hitting a "ceiling" as your rating gets higher: The game is out to get you and make you sad.
Another explanation for hitting a "ceiling" as your rating gets higher: At higher ratings, your opponents are better at the game, and maybe you are not actually the best in the world.
Which do you suppose is more likely?