I think there was a major leap from EVERY Beatles album to the next.
Unfortunately, in the cases of Beatles for Sale and Let It Be it was a leap BACKWARDS!!
I do agree that HDN is a better album than WTB.
Some of this is down to the band's progression. They were definitely improving as songwriters, for instance, and they were learning more about how to work in the studio as they spent more and more time there.
But WTB was at something of a disadvantage - HDN included two hit singles and their B-sides, whereas on WTB they stayed clear of doing that. Imagine how good WTB would be if you ditched four of the weaker songs ...
I want to hold your hand
All I’ve got to do
All my loving
Don’t bother me
Please Mr Postman
She loves you
I’ll get you
You really got a hold on me
It won’t be long
Till there was you
Not a second time
That would be a great album!
HDN also has the advantage of having its own distinctive sound, with George's 12-string Rickenbacker all over it. I think that makes it stand out as an album as well.
And maybe it's also more familiar to us because of the hit singles and the fact that half of the songs were used in the film.