Here is the comparison b/n default max physical material and Corona material in viewport.

It will be nice to have viewport preview (reflections) in high quality mode. Latest max even supports bloom.
For those who argue about the use case, some projects we don't even render due to time restrictions and last minute changes. We use viewport previews.
So far we have been creating 2 scene files, one with max physical material setup for previews and one with corona for rendering if needed.
It will be really helpful if Corona have an option of high quality preview in viewports or at least a button to turn it on/off.