I'm not sure why Americans are so certain that their system of separation of powers is the right one. Most countries don't separate the executive and legislative like that. The executive is whoever can command the support of the legislative. If you think about the US system it makes no sense. An executive can just ignore the rules created by the legislative by just not enforcing it and the only means to stop that is a 2/3 majority in a body that by it's nature is not representative of the population but rather of States.
As far as I can tell the US system is designed for gridlock. Things like filibuster, lower house elections every two years, state elected upper body, electorate system are all designed to create girdlock.
While Americans as a whole are to blame for some of this they are working in a completely broken system. In tech we try not to blame a person when something goes wrong so we look at what process allowed this to happen. I think many of the US problems are explained by their underlying system which is basically a copy of the English one at the time of Independence with a monarch and a parliament. Unlike the English system though it barely evolved since then.
The difference is in cases where the parliament chooses the executive is it leads to it's own collusion and corruption in terms of excessively growing govt... not that it's barely held the US from doing so. The point is to be in an adversarial context in order to resist overreach of govt.
For better or worse, our system today isn't quite what it was originally designed as... The Senate was originally selected by the state govts, not direct election... the Vice President was originally the runner-up, not a paired ticket and generally hamstrung as a result. The VP didn't originally participate in the Senate either, that came after WWII.
The good part about the constitution is there is a reasonable set of ground rules for changing said constitution with a minimum that should clearly represent the will of the majority of the population. (corrupt politicians not-withstanding)
> As far as I can tell the US system is designed for gridlock.
At the federal level the US system was designed for gridlock on purpose, with the premise that something shouldn't be federal policy without widespread consensus, and without that consensus it should be left to the states.
The problem is really that many of the gridlock-inducing measures have been thwarted, e.g. delegation of rulemaking power from Congress to the executive and direct election of Senators to prevent state-representing Senators from voting down federal overreach. But those things weren't just there to induce gridlock, they were also the accountability measures, so without them you put corruption on rails and here we are.
The structure of British government during the Hanoverian times was little different from what the UK has today. The monarch was effectively a powerless figurehead and executive decisions were made mostly by faceless very wealthy individuals in back rooms with the public face carried by a small set of charismatic figures who usually sat in parliament.
The US system was designed as a grand experiment. It made a certain amount of sense at the time: the country as a vast plantation steered by a benevolent master with policy set by wealthy landowners and businessmen who knew what was best for everyone. It was a system already in place in the Americas for generations and most national arguments could be hashed out at the club over some fine imported brandy or, for people like Franklin, some imported tea.
As far as it goes, there have been worse set-ups.
The filibuster isn't part of the system; it's not even part of the law. It's just part of the rules that the Senate chose for their own internal procedures.
I think it's designed that way because it wasn't originally seen as one country, more as a federation.
Even by the time of the civil war, Robert E Lee decided he was Virginian ahead of his national identity.
If you have a bunch of sovereign states, then you need some state-level evening out. If everyone is a citizen of one large state, you can just go proportional.
On top of this, it was never going to be easy to gradually move from one to the other with the issue of slavery looming large, so they didn't fix it. This was still a huge issue in 1848 when a lot of Europe was grappling with how to do a constitution.
So it stayed broken and here we are.