>He claimed (though I'm certainly no expert) that you have to do your own taxes and set aside money for that;
Unless you're a contractor, small-business owner, or some other sort of self-employed, no. Taxes are deducted automatically from your paycheck by your employer from every paycheck. At the end of the year you need to file a tax return, and you can do this yourself for free. But even most paid tax return services usually only cost ~$50-$150 for the average worker.
>he also claimed that "sales tax" had local, state and federal taxes applied, so while it varies from state to state and city to city; it generally ends up being about 18-20%, which is in-line with VAT in most Euro countries. And, as a general rule, a state with higher sales tax will usually have lower (or no) state income tax, and vice versa.
There is no federal sales tax in the US. It does vary from state to state, but it ranges from 0% to ~10%, nowhere near 20%.
>He made a lot of comments about certain mandatory insurances
The only mandatory insurances are car insurance (and even then it's only mandatory if you want to drive a car) and health insurance (and even that has only been mandatory since the ACA passed, and all the enforcement provisions of that have been gutted). The cost to an employee for decent health insurance is usually going to range from $0 a month to a several thousand a month, but the average is something like ~$700 a month for an individual to get coverage and ~$1,400 for family coverage.
Public transport outside of major cities does suck, but I don't think that's easily fixable. Something a lot of Europeans don't realize is that the US is way, way, way, way less dense than Europe. The US has 33.7 people per square km, the entire EU is 116.2 people per square km. public transit isn't really feasible because the costs to provide it go up almost exponentially with lower population density.
>I'm not sure, I don't know everything, but after talking with him I didn't feel bad for being a "poor euro" anymore, because while the absolute "amount" of money he earned was much greater, the amount that he could actually use was lower.
Even after accounting for things in Europe like free healthcare, the actual amount of spending power the typical American has is actually still far, far greater than that enjoyed by the typical European. The metric you can look at to see this is consumption: ~$38,000 per capita for the US in 2017, vs $28,000 for Switzerland, $23,000 for the UK, etc.: https://en.wikipedia.org/wiki/List_of_countries_by_household...
PPP and other factors make a one-to-one comparison difficult, but Americans have far more spending money left after taxes, and that combined with them making more money in general makes Americans far more wealthy. Especially in the software dev industry.