As I wrote, 52x11 on the Birdy is only 6.76m which is very short.

The Riese & Müller Birdy has 7.86-2.21m with a 9-32t cassette, a Brompton 6s with BWR 7.95-2.63m.

Neither the Birdy nor the Brompton are race bikes but nevertheless, their manufacturers judge that 7.86 and 7.95m are good for their bike. But maybe these manufacturers are incompetent ?

Shimano had Capreo with 9t smallest cog, SRAM introduced 10t cogs for both road and MTB on all their drivetrains but maybe Shimano and SRAM are incompetent too?