GDP isn't wealth, it is a measure of output over a period of time (and wealth is an amount at a point in time). It is also, generally, quite misleading because a nation can produce a tremendous amount of output, and all of that can be siphoned into an offshore account in Switzerland (KSA is an example, but there are also more subtle examples like Germany).
And measuring wealth is very, very complex. Do you include pensions? How do you value a state pension? Do you include housing? How do you value housing? But if you look at relative net financial wealth (inc. pensions, you are likely going to Google and find something that doesn't include pensions) then the statement is true...the US and Switzerland are way out ahead on net financial assets, and in datasets that include pension wealth then you have Australia up there too (which has one of the most successful pension systems in the world, very strong economy too but they punch above that weight when looking at wealth).
Again though, measuring these kind of things is complex so you have to not only be able to Google a ranking system but understand exactly how the pension system is structured in that country, how is the financial sector structured, how is the tax system structured, etc. The US is consistently at the top by any measure though.
The problem is that you're saying it's very hard to measure wealth while at the same time confidently claiming the US is at the top. That just doesn't make sense.
GDP may not be a perfect measure of wealth but it's the best we've got IMO.
I've lived for a short while in Canada, for many years in Australia, and visited the USA many times... I really don't see much difference in wealth in general. I'm sure there's a lot more extremely rich people in the USA, but those are a small portion of the population so I wouldn't consider that an important indication of the wealth of a country, at least not as much as the wealth of the majority of its citizens (and the USA notoriously also has a lot more very poor people than either Australia or Canada). If you do that, perhaps the Arab Emirates would be wealthier? Or even China, home to more bilionaires than the USA IIRC?!
Also, if you include healthcare access and pension as you seem to be doing, again, the USA is probably the worst as you're pretty much on your own with those things, while in nearly any other developed country, people get decent healthcare and pension even without having had high paying jobs their whole life.
And measuring wealth is very, very complex. Do you include pensions? How do you value a state pension? Do you include housing? How do you value housing? But if you look at relative net financial wealth (inc. pensions, you are likely going to Google and find something that doesn't include pensions) then the statement is true...the US and Switzerland are way out ahead on net financial assets, and in datasets that include pension wealth then you have Australia up there too (which has one of the most successful pension systems in the world, very strong economy too but they punch above that weight when looking at wealth).
Again though, measuring these kind of things is complex so you have to not only be able to Google a ranking system but understand exactly how the pension system is structured in that country, how is the financial sector structured, how is the tax system structured, etc. The US is consistently at the top by any measure though.