Metal isn't new, it's older than Vulkan, and by some metrics I would consider it better.
For one, the learning curve is much smoother: you can get something up on screen quickly, but only later discover the advanced features like argument buffers, manual hazard tracking, etc.
We are talking 4 years old (3 for desktop) years old vs 2 years old, you're kidding yourself if you think either is established by virtue of being old vs new. That comparison was only fair with OpenGl.
For one, the learning curve is much smoother: you can get something up on screen quickly, but only later discover the advanced features like argument buffers, manual hazard tracking, etc.