It's just when they did stadiums and the technology just wasn't there to justify those performances, andthe Beatles indeed not able to hear themselves over the screaming girls, who really probably weren't even sure what those guys were playing or cared honestly. That demoralized the band, and they got sloppy in just not even trying anymore.
I bought a book years ago, "Beatles Gear," which showed the equipment they used throughout their careers. Your statement, "the technology wasn't there," was an understatement. They had been using 50-watt amps until their Shea Stadium (NY) concerts, then they got Peavey (I think) to make 100-watt amps. They needed them, too, because the concerts were piped over the stadium's PA system, normally used to announce the batting order for baseball games. Not exactly a superior auditory experience for their fans and them. Also, they didn't use foldback speakers then, which meant they couldn't even hear what they were playing.
