the claim in the OP is "1/3lb burger failed in america

It did, in the 80s, when A&W tried to sell them. I live a 30m drive from the original A&W, they have newspapers up from that time with the people bitching about it. It's a popular "fun fact" style story and has been since it happened

The practice wasnt successful until the early 2000s, a little after it had become a fun fact that became more and more widely known. I think I even remember seeing an ad for Carl's Jr that played on the fact that A&W had failed where they were succeeding and made some joke about dumb older generations or whatever to appeal to the youth