http://blogcritics.org/the-beatles-many-drummers/
The beatles had at least 6 drummers.
They had 4 drummers while they had Ringo.
They replaced Ringo for one major tour.
The movie spinal tap is a parody of the rock and roll music business. They had 10 drummers in spinal tap.
In my most successful band During the course of 1 year playing every weekend and sometimes 3 days a week. We used 6 drummers and 3 singers.
The bass player, me, and 2 guitarist played every show. We all had steady day jobs except for 5 of the drummers.
In a 50 year music career from the time I was 13 to now age 63. Every band I have been in has always had multiple drummers.
I don't think any band want's to have more than one drummer.
It is just the nature of the beast.
To have a band you have to have several people that can make music. When you loose them you loose the band. And then after you have people that can make the music. You need someone who can keep a beat.
A band can replace a drummer on the fly. You can't do that with a guitarist, bassist or singer.
I have my own recording studio. I can listen to any song and sit down and play the drums right after listening to the song.
You can't do that with the guitar or bass. It might take hours to copy a guitar solo or bass part.