yes we know that. the bay city rollers were bigger in there day than the beatles were in there day like it or hate it it's a fact
I guess it's important to define "bigger".
Comparing them in anything other than teen girl mania (for a few years) is a stretch.
While Bay City Rollers sold a good number of records for a short while, they were a very different cup of tea than the Beatles, if there is any doubt, listen to the catalog of songs written by the two bands while checking the net worth of the members of each band.
Bay City Rollers broke through in early 1975 in the UK and late in 1975 in the USA.
They had two Billboard hits in the USA and were popular worldwide in 1976, ...a decade later nobody in the USA remembers any song from them but "Saturday Night".
In 1976 & 1977 members were quitting over embarrassment, and being replaced.
By 1977 their popularity had waned.
By 1978 they were two competing bands.
They were a flash in the pan boy band popular with young teen girls for a couple years.
They garnered no respect from other musicians or any teen/young adult who was into music at that time.
They had no influence in shaping popular music in the 70's or the years since then.
Like these bands did:
AC/DC
Aerosmith
Alice Cooper Band
Allman Brothers Band
Black Sabbath
Chicago
The Clash
David Bowie
Deep Purple
Fleetwood Mac
Jethro Tull
Kiss
King Crimson
Led Zeppelin
Pink Floyd
Queen
Ramones
Rolling Stones
Santana
Sex Pistols
Bruce Springsteen and E Street Band
Steely Dan
Van Halen
The Who
Yes
And 20 other bands not mentioned.