It’s better than SYD Intl J lounge. And let’s not even bring up MEL Intl J.Yes, that lounge isn't bad ... for a Nth American lounge. But for me, a great lounge does not a great airport make. For me its about the core function of getting me on and off an aircraft in as best condition as possible. And my last 3 experiences there have been pretty bad.
I don’t know objectively what your problem is with MIA. It has a good train connecting gates, modern concourse with good shopping and dining, multiple AA lounges - as a “North American” (your words) airport, I think it’s definitely above average.