I think a lot of people are extrapolating from their experience with monoliths and imagining that Monzo devs are maintaining 1600 tiny monoliths. That's an anxiety-inducing thought.
I would prefer maintaining a "tiny monolith" over a micro service. At least with the monolith you're writing value-delivering business-logic code. From my experience with micro services you spend more time on boilerplate and the whole HTTP/RPC part and the communication with other services than the actual task the service is supposed to be doing.