I'd have to agree with those comments your girlfriend made, it blatantly obvious to anyone, even the most ardent U2 fan, than Bono doesn't have the same power and energy he used to, but that has nothing to do with his vocal ability, range etc. I'm sure he can still sing songs in a similar way, with the same tone, vocal range etc, what he can't do is put as much power and force into that voice as he used to. There are some exceptions like Ultraviolet, Miss Sarajevo, Streets, TUF, but I just can't imagine Bono singing God Part II, Angel of Harlem, Night and Day, Pride, Hawkmoon etc, in the same way he did in the 80s and 90s.
That isn't a criticism, just a fact, he is older now and we all know the history with his vocal chords, being allergic to red wine, smoking etc. It's just wear and tear and age, he won't be recording vocals like those I've mentioned, in addition to In A Lifetime, With Or Without You, Desire, Who's Gonna Ride Your Wild Horses...
1.)You have a long list of exceptions!
2.)Pride, Angel of Harlem the same way as the 80s and 90s? Pride he screamed and rarely sang with any kind of power or conviction at all in the 80s and it was pretty flat in the 90s, though pretty good on Zoo TV. It was only really great on Conspiracy of Hope and Vertigo. Angel of Harlem was definitely best on Lovetown, but the band has not even done it in the same style since then and far be it from any of us to know why. The Lovetown performances of AOH were criticized as pompous, maybe part of why it has subsequently been toned down a bit or a lot, depending on the tour. In fact, the somewhat lackluster 90s Zoo TV versions were easily topped in terms of vocal range and power on the last leg of Vertigo and on 360 to a lesser extent.
3.)Perceptions of the average person do not tell us the actual situation. Most people do not really analyze this stuff, and often can mistake screaming for power.
4.)Vertigo(feeeeeeeeeeeeeeeeeeeeellllllllllllllll), Original of The Species, Sometimes, No Line On The Horizon, Magnificent, Moment of Surrender, White As Snow, Cedars of Lebanon(lower register) are all on par with the studio moments that you can't see him matching.