It's not naive, it's correct. GNU's focus is on features, kitchen sink style, performance tuning, etc. If that's what you want, it's for you. OpenBSD is focused on correctness. It's not correct to use hacks and buffering in tools to increase performance. That should be handled at the syscall interface or in the kernel or whatever.
Can you expand on why you think performance hacking degrades correctness? As I understand it, “yes” (with no arguments) is supposed to output “y\n” continuously until terminated. Throughout/latency are unspecified, admitting various implementations with various concerns, like GNU’s focus on throughout vs BSD’s focus on latency/simplicity. Even an implementation that took 10 seconds between each output could be desirable for some use cases! Is that version of “yes” less correct?
The case can be made that, given that kernel code tends to be more difficult to write and debug and is inherently security critical, there ought to be less of it. If the buffering can be generalized then it ought to be in a library to be shared, otherwise the application is the right place.