Indeed it has been discovered by massive-mass tourism. Some places are pretty much lost to that, like the Trevi Fountain and parts of the Forum.
But it depends on how you conceptualize your Roman holiday.
As I grow older, I am less and less interested in sightseeing and more and more into sampling a different lifestyle. Sights are just changing backdrops.
For my purpose, Rome remains a delight. I'm enraptured just to walk and walk and, go to the market and buy in-season ingredients and try out Roman recipes at home, or get ourselves adopted by a caffé and sit there vegetating, doing nothing. -- In fact all the cities I love have to have this doing-nothing factor. Which cities keep you coming back, delighted doing nothing? For me Rome is one.
Even in Rome, even in the thick of tourism max-out, we don't have to be part of the problem (and complain about the problem) if we don't want to.
Last time I was in Rome, which was a little over a year ago, we braved the Vatican museum, as we had not visited it for the previous few trips.
The crowd in the Sistine Chapel was terrifying indeed. Then somehting miraculous happened: A biblical exoduns. All the tourists filed out of a side-door, which I later learned was the "Steve Ricks Sistine side-door". We decided not to follow the crowd and to walk the long way (not that long, about 20 minutes) back to the museum exit.
There we were, all alone, wandering from one deserted room to another, DESERED!, while everyone else was off to the next Ricke Steves highlight. -- I respect Rick Steves for many things. We should bear in mind that his forte is in giving non-experts a nicely streamlined concept of a visit. Being a non-expert in everything, I have benefited from his information on many travels.
And Rick Steves is global. Everyone follows him. Other guidebooks in other langauges copy him. So you have this phenomenon where the entire world converges on a couple of rooms in the Vatican or a few corners of the Forum, and just one room away or around the corner, the place is empty and is all yours. I aspire to making a film-negative-like inverted-black-white map of Rick Steves tourist maps. My maps will show people where Stevists don't go and I'll make a zillion euro. You are all welcome to invest in the Parigimaps series.
By the way we're going back to Rome this xmas-new year. Can't but can't wait.