I guess you know best, but Steinberg seems to disagree with you:
"[…] ASIO (Audio Streaming Input Output) is a technology of Steinberg.
It allows for low latencies and pretty much every state-of-the-art audio device is nowadays delivered with an ASIO driver (on Windows, at least). > However, the basic idea behind ASIO is
that professional audio applications entirely take ownership of the ASIO device. Only very few ASIO drivers support true multiple application access.
This effectively means that you can not use 2 or more applications using the same ASIO device at the same time.
This from the readme that accompanied the unofficial multi-client driver made by Charlie Steinberg himself.
I guess most modern soundcard manufacturers have since solved this issue themselves, like RME did.
However, my point was the difference in design philosophy between ASIO and CoreAudio. The former, like Steinberg says above (highlighted), is designed for maximum performance with a single application, whereas CoreAudio is meant to provide professional grade low-latency audio system-wide. And I maintain that this somewhat (but not completely) explains Cubase’s performance deficit on OSX.
Just google ASIO multi-client if you want to get the whole picture.