Noble Knight will never be T1 because they released multiple copies of "Eternal Rest" at the same time. It's pretty much the equivalent of Acid Rain when Ancient Gear decks were popular.
"Noble Knight will never be T1 because they released multiple copies of "Eternal Rest" at the same time." --> No one is using Eternal Rest, and no one used Acid Rain.
And adding to that, no one is using Eternal Rest because it only counters Noble Knight and nothing else. Making it useless when you doesn't encounter NK player for 10 duels straight.
It's for the same reason AG didn't die down because of Acid Rain. No one ever use Acid Rain to begin with. The real reason AG deck went down is because newer and better decks are released.