Exactly. It was really the combination of two or three talented people feeding off each others' creativity. John/Paul each 'only' had to write 3-5 songs per album, with George filling in some extras. I'm not saying it's
easy to write 3-5 good songs, but they had a knack already. One person trying to write 12-14 good songs per album is facing an impossibility - and we can see that with their solo albums. Most of them have a handful of good/great songs, and then... relative filler.
Each Beatle album getting the 'best' of a group of talented writers was the magic sauce, imo.
But even then, the pace was still... insane. Tour in the 1965 summer time, come back to UK, start writing an album in October, work for a month, and put out Rubber Soul, nearly all of which was written and recorded in that single month. That is possibly the most creative/productive single month in their career.