It also provides a way for a pseudo-microkernel like architecture despite Linux, as many services run on their own process talking with the Linux kernel via Binder.
IIRC, Binder also still includes "passing" the scheduler quanta between procese6when making a call - meaning that when you make a call from process A to process B, instead of waiting for process B to be scheduled for execution, it is swapped in place of process A in scheduling - effectively, process A "pays" for the CPU tone that process B needs to service the call.
How do they ensure this under Linux?
They don't. There is some notion of priority boosting but with everything running as sched_other it does essentially nothing.
After extra checking, yes, they hack around a lack of infrastructure on kernel through tricks with setting nice values - I do know of patches that implement more, but they ultimate never got upstreamed