It doesn't make sense to compare the EU to a federation with more than double its land area, composed of 50 different states, which are quite different from each other in a large variety of salient ways.
If you drop Mississippi, Idaho, West Virginia, Arkansas, South Carolina, and Alabama from the US numbers, then the US GDP per capita number would look bigger. Anyone can get different numbers by cherry-picking higher performers and dropping lower performers, but OP wrote "Europe" not "this list of rich countries in Europe".
So the comment you're replying to was correct, for at least one plausible definition of "1/3 lower than the US".
As for the countries you mentioned:
Monaco: < 1 square mile, not reproducible in a larger country
Norway: Giant oil reserves / tiny population, not reproducible without that
Switzerland: Valid
Ireland: GDP numbers shouldn't be taken at face value because tax laws[2] encourage corporations to attribute EU-wide revenues to Ireland. Reported GDP per capita is 135% of the US value, but 2016 median household income[3] was only 87% of the US value[4]. This cuts both ways, though - other EU countries should have their estimates nudged upwards.
Iceland: 92% of US GDP per capita[1]
Denmark: 91% of US GDP per capita[1]
Sweden: 86% of US GDP per capita[1]
Austria: 91% of US GDP per capita[1]
Finland: 79% of US GDP per capita[1]
UK: 75% of US GDP per capita[1]
France: 74% of US GDP per capita[1]
Italy: 68% of US GDP per capita[1]
Spain: 65% of US GDP per capita[1]
EU (all 28 countries): 71% of US GDP per capita[1]
(USGDPPC - EurozoneGDPPC) / AVERAGE(USGDPPC, EurozoneGDPPC) = 0.283
Roughly speaking, you could write this as "The GDP per capita of the Eurozone is 28.3% lower than the US".
[1] https://stats.oecd.org/Index.aspx?DataSetCode=PDB_LV