I think it really depends on what people are specifically referring to. In a broad sense, virtually all rock music is technically "melodic rock" because music is melodic by definition (ruling out extreme and experimental sub-genres, of course).

I'd be surprised if anyone here doesn't know that The Beatles were extremely influential on music and pop culture in general. That's why I thought the question was more about that specific "melodic rock sound" that this site celebrates. Things like high-pitched vocals, guitars with the right amount of bite and crunch, keyboards that usually have a more electronic/processed sound rather than traditional piano, drums with punch and reverb, songs that tend to be layered and have some instrumental "showing off", etc. The Beatles definitely brought harmonies into the mix more than predecessors like Elvis Presley, Little Richard, Chuck Berry, and Buddy Holly, but all of those artists (as well as others that I didn't even mention) had melodies, guitars, pianos, catchy songs, etc. The Beatles played a major role in music's progression, but I don't think it can be said that The Beatles were the moment when melodic rock went from not existing to existing.