Ringo was sad because Paul was dead. Look at the early footage of Paul, then there's a little break where they announced the Beatles wouldn't play out anymore, then the bearded, 3" taller, 20 pound heavier, old lady faced Faul is the rest of the show. (Paul and John were the same size, could wear each other's suits.)
Billy could adopt anyone's singing style, his dad was a music professor, he was an accomplished pianist. He was a perfect stand in after some surgery.

The three were demoralized.

And may I introduce to you,
the one and only Billy Shears
and Sergeeant Pepper's Lonely Hearts Club Band..


Faul was a good pianist- Paul was not.
Faul made a string of cover singles under the name of
Billy and the Pepper Pots.

Don't bother trying to tell me otherwise, I've known this for 50 years now.