The article compared the market cap of Tesla to Hong Kong's GDP. I stopped reading then.
Governments already operate mostly near maximum revenue. Raise taxes anymore and Capital and labor walk away.
Look at OECD data on tax revenue as percent of GDP [1]. France is at the top at 46.1%. OECD average is 34.2%. US is near the bottom at 26.8%.
Given the big differences in tax rates, it seems implausible every government is at maximum revenue - that might be true for the highest taxing countries like France and Denmark, but is unlikely to be true for a below-average tax country like the US.
The “Laffer curve” determines maximum government revenue - the point at which raising taxes any further would cause overall government revenue to fall. Nobody knows exactly where that point is, but most experts believe the US is a fair way below it (see e.g. [2])
> This indicator relates to government as a whole (all government levels)
"all government levels" means state/provincial/territorial/regional/county/city/town/etc, the whole lot
So I see no evidence it is “misleadingly low”, I think the OECD’s statistics are generally accurate. (More accurate than the UN’s, because the countries whose governments are most likely to commit statistical fraud are not OECD members.)
If they compared Saudi Aramco's revenue with Hong Kong's annual GDP, that would make a bit more sense since they're both annual figures.