Spacca Napoli is an interesting case in point. They do have a proper Neapolitan oven which bakes a pie in 40 or so seconds. But things rapidly deviate from what I have come to understand as authentic from there. They have a diving arm mixer which is second best apparently. They have imported an Italian pizzaiola vs a Neapolitan one. Consequently they are not using some of the authentic ancient dough methods I have read about here from pizzanapoletana (which have subsequently been largely deleted for some reason). They do not use wild yeast consequently their crust is devoid of any substantial flavor. Their bufala soaks the middle of their unsliced Margherita. Adding all that up, they still produce a pie which kills UPN but not one which I would say is truly authentic. But since I have never eaten an authentic pie, all my points are opinions at best.
Being a pizza neophyte and a relative newcomer here, I'm not sure I have all my facts down straight. But if you are talking about Spacca Napoli in Chicago versus Una Pizza Nepoletana in New York, I don't think I could disagree more. Jonathon Goldsmith, the owner of Spacca Napoli will flat out tell you that he is at the start of a long path to discovering how to make his ideal Neapolitan pizza. He is an enthusiastic newcomer with amazing drive and a passion to make the most authentic and best pies possible. However, his pizza is a far cry from the ones I've had at UPN, strictly on taste alone and NOT on anything dealing with the pizza's authenticity. Spacca's ingredients, IMO, are a long way from what Mangieri is serving up at UPN, regardless of where they come from. If authenticity is the main criteria here, then disregard anything I've written. My main point is that, regardless of how it's made, UPN makes significantly better bread (crust) than Spacca Napoli.
Some have suggested above that UPN has recently been going downhill and since I haven't eaten there since last May, I can't comment on that. But it would have had to really tank to have gotten to Spacca Napoli's very respectable level, just based on the flavor of the crust alone.