Even the executive being separate from the head of the legislative branch is uncommon everywhere else.
The Presidential System (as distinct from the Prime Ministerial System) is common throughout Latin America and West Africa. Incidentally, it is also a governmental structure more vulnerable to coups and similar violent takeovers, as the President being in conflict with the Legislature often leads to these snap power grabs rather than more well-defined transitions of power after elections.
The US idea that the different branches would have checks and balances against each other was rendered pointless the moment the first political parties were developed.
Well, that’s another big difference between the US system and systems in countries with more settled populations. Regional parties (the Scottish National Party being a large and distinct block of voters in the UK, the uMkhonto weSizwe as a Zulu nationalist group in South Africa, the Taiwan Solidarity Union as a Taiwanese nativist faction, or Otzma Yehudit in Israel which draws its doctrine from a single ultra-nationalist Rabbi Meir Kahane) can all exist in parliamentary systems in a way that a Mormon Party or a Texas Party or an African-American Party has failed to materialize in the United States.
The idea of checks and balances doesn’t work when you’re forced into coalition with one of the two dominant (heavily coastal) parties to have any sway in Congress or within the Presidential administration. And that goes beyond just “Voting for President”. The Democrats don’t nominate bureaucratic leaders (Sec of State, Attorney General, etc), the President does. This gives enormous influence to a singular individual who functions as both Party Leader and National Leader.
Compare this to Brazil or Germany or India or Israel, where power-sharing agreements between caucusing parties encourage the incoming Prime Minister to choose from the leaders of aligned party groups to fill cabinet positions. There’s an immediate payoff to being the head of a small but influential partisan group under the PM system in a way that the American system doesn’t have.
Now, do you want Anthony Blinken or Janet Yellen to have to hold a Congressional seat and act as Secretary of State or Secretary of Treasury? Idk. I’ve seen Brits scoff at this system as being its own kind of mess. But I can imagine a country in which a Yellen-equivalent head of the Liberals for Better Economic Policy Party has half a dozen seats and Blinken’s Americans for NATO Party has half a dozen seats, and this is what Biden needs to be Prime Minister, so he appoints them to his cabinet as a trade-in for their support.
