Under the tax treaty between Italy and the US, you tend to pay the higher of the two rates (except for SS/government pensions, I think, which default to the US treatment). I don't believe there is an 85K exemption threshold -- Sounds like eastbayboy may know the exact details. You may be thinking about the Foreign Earned Income Exclusion, which usually is not triggered by people under FIRE (passive income is ineligible). In Italy there is a pensioner exemption of like 7500-7700E and some partial deductions for things like health insurance and mortgages, I believe (and other deductions). The Italian rates can get pretty high, pretty quickly but passive income is treated with a (higher) flat rate.
Italy has a wealth tax on overseas investments of 0.2% (relatively low, and I believe 401K/IRAs may be exempted) and overseas properties of 0.76% (choice of original or current gross value, with a possible credit for property taxes). Several other countries have wealth taxes, although there is often a relatively high exclusion amount and similar credit schemes. Note there are property and stamp taxes on Italy resident assets as well.
This is why the tax schemes can be attractive for those that want to live in Italy. However, many just go ahead and pay the extra cost, as the want to enjoy the life there and understand services come with a cost.
I know of Americans who initially picked Italy but moved to places like Menton, just over the Italy-France border. Due to the tax treaty differences, the savings can be considerable.