Absolutely behind the times. No SMP, OpenGL isn't fully supported, Flash support sucks.
But if you're going to try to use an Amiga like system for modern computing, then NG OS' are light years past legacy systems in performance.
You can't convince me that a legacy Amiga can be upgraded to the point where it becomes a viable platform for modern computing. All three NG OS' are capable of performing at least adequately.
And I don't care what is and what is not a legitimate 'Amiga'.
I'd use an NG system or emulation rather than suffer with the poor performance that is inherent with legacy hardware.