To be clear what I originally said was "1E is the only version that was more popular than 5E is (at least in print sales)."
I do not believe for a second that WOTC has sold more 5E material in print than AD&D 1E and all the versions of BECMI. I don't think 5E has sold as much printed material as Dragon magazine alone did during 1E.
TSR sold around 3M copies of the various basic sets (not including Expert, Companion or any AD&D stuff) and Dragonlance sold 30M products (to be fair, this includes the novels).
I can believe that more people play 5E than played 1E, but I don't think there are as many sales and I know there are not as many print sales. You mention DND Beyond and most of those 10M probably have access to a ton of books they have not purchased. For example, I know I have access to all the WOTC books on DNDB and most of the 3rd party books and the only electronic books I have purchased are: PHB, SODQ, VGM and OOTA. 3 months ago the only book I had on DNDB was SODQ.
This is before you consider how ubiquitous unauthorized/unlicensed material has become. My son and daughter both play in regular games with their friends and they do not use any purchased material. They use one of the pirate Wiki sites (which will go unmentioned) to build characters, select spells, subclasses etc and use other online resources for monster stat blocks.