Beatles played to an America where 28% more households had a TV. But the Beatles' audience was only 22% bigger than Elvis'.
And that doesn't even account for the fact that the Beatles' *potential* audience was WAY bigger - by maybe 20 million people, AND thanks to the post-war baby boom, they had a much bigger % of that bigger audience who were teens.
TV viewership just seemed like an easy and fair metric for "popular." If the question is "most influential," I agree it's the Beatles.
If we wanted to compare their number of #1 hits, Elvis is going to do very poorly. Consider that he was drafted and joined the army a mere 2 years post Ed Sullivan, and then his manager sent him off to Hollywood for a decade of schlock and cringe.
The 2018 documentary "Elvis the Searcher" on HBO spent a lot of time on this, and I think that's the lens I've always seen him through: he was gorgeous, he had an A+ voice, he was charismatic, he brought a new genre to Americans in a way that a single person has never done before or since. He had the most widely recognized name on the planet for a time... and then he just sort of pissed it away, he missed out on the musical explosion of the 60's, and he returned as a fat drug addict in a sequined jumpsuit, and since America loves nothing more than a profound fall from a really high place, he was the punchline of a million jokes from that day forward.