Firsty, let me say I am one of those that finds Macca's songs sublime. (I even find songs like 'Why can't we do it in the road' an interesting diversion.) I can say this because I like styles of music with very strong melodies and chord progressions that move outside of the diatonic - something The Beatles were inherently brilliant at. It's a generalisation, but today's I - V - vi - IV production formula is the antithesis of this. Melody has been forsaken for rhythmic, arranged production. The brilliant contemporary music is hidden and not often on the mainstream.
To some extent, my Brit background and age provide a fertile bed for The Beatles' music to be planted in. However, I wonder how much my favouring of their style of music allows me to exalt their songwriting to a level well above others? e.g. as a contrary, I am not a country music fan, so no matter how brilliant Garth Brooks is, I am never going to regard him highly. (Don't crucify me

) In reverse, I am sure this might be the case for a Garth Brooks fan as well. This is not discounting that McCartney (or Garth Brooks) has wide appeal.
Clearly, The Beatles were writing and recording at a time of extraordinary change in modern music and rode that wave all the way to the shore. While Lennon, McCartney and Harrison wrote some excellent songs post The Beatles, I can't quite say they hit the same high-water mark IMHO, but there are some good ones: Maybe I'm amazed; New; Every night; This never happened before. I wonder how much the cross-inspiration (competition?) between them drove them on. I have created some post-Beatles playlists combining the best of McCartney/Lennon/Harrison/Starr for each year from 1970 to 1980, and they still don't seem to match The Beatles' repertoire - at least from Rubber Soul onwards.
There would be nothing more *potentially* restrictive to a songwriter than the idea of a series of 'tools', techniques or tips. 'I'll just pull this songwriting screwdriver out of my bag.' However, there are many tutorials that describe the vast array of songwriting tips and maybe the vastness of the array means one doesn't over-rely on a narrow few, or the tool itself become sthe inspiration. I also understand why Sir Paul would want to stay away from a formulaic process. It could ruin the magic.
I think all songwriters stand on the shoulders of giants - meaning we are all building upon / being inspired by someone or something we have heard before. This is why I use BIAB - the many styles immediately take me out of my comfort zone to think of something I would never have. In one way, and understanding a little about Paul McCartney's upbringing and being immersed with Lennon and others from a young age, I can see how he may have been marinated in a very creative soup.
As a tangent, has anyone seen any analysis of songs Macca didn't write, but his talents brought those songs to perfection? e.g. I am thinking of his bass work on 'Something' or 'Hey bulldog'; his vocal harmony on 'Every little thing', 'Wait' or 'While my guitar gently weeps'.