The GP is not saying they aren't issues, just that they don't add much value to the conversation. It's especially clear in how it triggered your response... and in how you've mostly overlooked those same problems in Europe (with the minor nod on violence). I'm an American and European (yes, two passports) who has lived in three different major cities in the US, two in Europe in separate countries, and I've traveled extensively in both areas. Let me offer some counterpoints:
On healthcare, I've had to sit for 2-3 hours in an emergency room in London with my throat mostly closed struggling to breath because I hadn't turned blue yet (no kidding), which put me behind the people with stab wounds. That's a normal ordering of priority when there aren't any doctors available, but it was mostly because I was on a six-month waiting list to see an allergy specialist and hadn't yet been diagnosed. At least in the US, your only fear about getting sick is because you're worried about the cost. I had a xenophobic doctor (said I was just coming to the UK for the healthcare, hah, even though I was working and paying taxes) prescribe me medication I was allergic to despite saying over the course of several visits that I was. Luckily I looked up the medication before taking it.
As to homeless people, sure, there may be less in the cities (though still there), but in exchange you have shanty towns and cities setup on the outskirts like with Cañada Real outside of Madrid, or Christiania in Copenhagen. I've seen smaller ones in France (Nice and Paris), though at least one of them was removed, and know of short-lived ones (on the order of months and years) in London. On both sides of the pond you have people trying to make things better, like Utah's experiments or those of Helsinki.
As to violence, Europe is a dangerous place. If the people you've spoken to were afraid for the first time in their lives, that's mostly because people grow accustomed to their own brands of violence. I was about an hour away from being blown to bits in the 2004 Madrid bombings, I was lucky enough to have decided not to bring my family to the Promenade des Anglais in Nice the day the terrorist decided to drive his truck through the crowds, and I've experienced the terror that is walking through the streets of London at night during an uptick in knifings (never attacked myself, though a colleague was and escaped).
We can talk about the abduction of children like Madeleine McCann, or the acid attacks on people like Katie Piper. We can talk about the shootings in Northern Ireland, or the annexation of Crimea, but instead you should just look at the Wikipedia page on European terrorism, even though it's only one type of the violence you can encounter.
As to obesity in Europe: Yes, the USA is on top, though there are variations by city (and people trying to fix it), but I have seen people too fat to board a bus (and no, not Americans) in both England and France, at the least. Don't believe me? Look for pictures of Virginie Grossat, French (!) model size 54 (though I've never seen her in public, just ordinary people).
But what about your claim that Europeans measure their style of living by how the poorest people in their country live? What does that say when you look how the Syrian refugees were treated in Europe? Maybe they're discounted because they weren't citizens? Well then, how about how the Polish are treated in the UK and Ireland, or ex-colonial immigrants in France? What about eastern Europeans in general, or the Romani people?
None of this is meant to say that America is just great, or Europe just sucks (I happen to be very fond of both). Why do you think so many people emigrate to the US? What the grandparent was trying to say is that when creating this caricatured version of the US (or any place that happens to be "other"), then you end up engaging in the very thing you're decrying, "whataboutism", and you actually blind yourself to the reality.